Medical device and method for predicting cardiac event sensing based on sensing control parameters

ABSTRACT

A medical device is configured to receive sensed cardiac event data including a value of a feature determined from each one of a plurality of cardiac events sensed from a cardiac signal according to a first setting of a sensing control parameter. The medical device is configured to classify each value of the feature of each one of the sensed cardiac events as either a predicted sensed event or a predicted undersensed event according to a second setting of the sensing control parameter that is less sensitive to sensing cardiac events than the first setting. The medical device is configured to determine a predicted sensed event interval between each consecutive pair of the predicted sensed events and predict that an arrhythmia is detected or not detected based on the predicted sensed event intervals.

This application claims the benefit of U.S. Provisional PatentApplication No. 63/060,773, filed on Aug. 4, 2020 and entitled “MEDICALDEVICE AND METHOD FOR PREDICTING CARDIAC EVENT SENSING BASED ON SENSINGCONTROL PARAMETERS,” the entire contents of which are incorporatedherein.

TECHNICAL FIELD

The disclosure relates generally to a medical device and method forpredicting cardiac event sensing according to different sensing controlparameter settings.

BACKGROUND

Medical devices may sense electrophysiological signals from the heart,brain, nerve, muscle or other tissue. Such devices may be implantable,wearable or external devices using implantable and/or surface (skin)electrodes for sensing the electrophysiological signals. In some cases,such devices may be configured to deliver a therapy based on the sensedelectrophysiological signals. For example, implantable or externalcardiac pacemakers, cardioverter defibrillators, cardiac monitors andthe like, sense cardiac electrical signals from a patient's heart. Amedical device may sense cardiac electrical signals from a heart chamberand deliver electrical stimulation therapies to the heart chamber usingelectrodes carried by a transvenous medical electrical lead, anon-transvenous medical electrical lead or leadless electrodes coupleddirectly to the housing of the medical device.

A cardiac pacemaker or cardioverter defibrillator may delivertherapeutic electrical stimulation to the heart via electrodes carriedby one or more medical electrical leads and/or electrodes on a housingof the medical device. The electrical stimulation may include signalssuch as pacing pulses or cardioversion or defibrillation shocks. In somecases, a medical device may sense cardiac electrical signals attendantto the intrinsic or pacing-evoked depolarizations of the heart andcontrol delivery of stimulation signals to the heart based on sensedcardiac electrical signals. Upon detection of an abnormal rhythm, suchas bradycardia, tachycardia or fibrillation, an appropriate electricalstimulation signal or signals may be delivered to restore or maintain amore normal rhythm of the heart. For example, an implantablecardioverter defibrillator (ICD) may deliver pacing pulses to the heartof the patient upon detecting bradycardia or tachycardia or delivercardioversion or defibrillation (CV/DF) shocks to the heart upondetecting tachycardia or fibrillation.

SUMMARY

In general, the disclosure is directed to a medical device system andmethod for analyzing sensed cardiac event data for evaluating thesensing performance according to at least one alternative sensingcontrol parameter setting. The sensing control parameter may be aprogrammable sensitivity setting used to sense intrinsic cardiac eventsattendant to the depolarization of the myocardial tissue, e.g., R-wavesattendant to ventricular depolarization and/or P-waves attendant toatrial depolarization. A medical device system operating according tothe techniques disclosed herein senses cardiac events according to aprogrammed sensing control parameter setting and stores a feature ofeach sensed cardiac event. The medical device system may classify eachof the stored event features as being a predicted sensed or a predictedundersensed cardiac event based on at least one different setting of thesensing control parameter. The different setting of the sensing controlparameter may be less sensitive to sensing cardiac events than theprogrammed sensing control parameter setting used to sense the cardiacevents. The medical device system may determine when an arrhythmiadetection is predicted based on the predicted sensed events and/orpredict a therapy response to the predicted sensed events. For example,the medical device system may determine a time interval required todetect a tachyarrhythmia episode according to at least one differentsetting of the sensing control parameter for comparison to atachyarrhythmia detection time according to the programmed sensingcontrol parameter setting.

In one example, the disclosure provides a medical device including aprocessor configured to receive sensed cardiac event data. The sensedcardiac event data includes a value of a feature determined from eachone of multiple cardiac events sensed from a cardiac signal according toa first setting of a sensing control parameter. The processor isconfigured to classify each value of the first feature as either apredicted sensed event or a predicted undersensed event according to asecond setting of the sensing control parameter. The second setting isless sensitive to sensing cardiac events than the first setting. Theprocessor is configured to determine a predicted sensed event intervalbetween each consecutive pair of the predicted sensed events and predictthat an arrhythmia is detected or not detected based on the predictedsensed event interval. The processor generates an output based on thearrhythmia detection prediction associated with the second setting ofthe sensing control parameter.

In another example, the disclosure provides a method that includesreceiving sensed cardiac event data that includes a value of a featuredetermined from each one of multiple cardiac events sensed from acardiac signal according to a first setting of a sensing controlparameter. The method further includes classifying each value of thefirst feature as either a predicted sensed event or a predictedundersensed event according to a second setting of the sensing controlparameter. The second setting is less sensitive to sensing cardiacevents than the first setting. The method further includes determining apredicted sensed event interval between each consecutive pair of thepredicted sensed events and predicting that an arrhythmia is detected ornot detected based on the predicted sensed event intervals. The methodincludes generating an output based on the arrhythmia detectionprediction associated with the second setting of the sensing controlparameter.

In another example, the disclosure provides a non-transitorycomputer-readable medium storing a set of instructions which, whenexecuted by a processor of a medical device, cause the medical device toreceive sensed cardiac event data including a value of a featuredetermined from each one of multiple cardiac events sensed from acardiac signal according to a first setting of a sensing controlparameter and classify each value of the feature as either a predictedsensed event or a predicted undersensed event according to a secondsetting of the sensing control parameter. The second setting is lesssensitive to sensing cardiac events than the first setting. Theinstructions further cause the device to determine a predicted sensedevent interval between each consecutive pair of the predicted sensedevents, predict that an arrhythmia is detected or not detected based onthe predicted sensed event intervals, and generate an output based onthe arrhythmia detection prediction associated with the second settingof the sensing control parameter.

In another example, the disclosure provides a graphical user interfacesystem including a processor and a display unit coupled to theprocessor. The processor is configured to receive sensed cardiac eventdata including a value of a feature determined from each one of multiplecardiac events sensed from a cardiac signal according to a first settingof a sensing control parameter. The processor is configured to classifyeach value of the feature as one of a predicted sensed event or apredicted undersensed event according to a second setting of the sensingcontrol parameter. The second setting is less sensitive to sensingcardiac events than the first setting. The processor is configured todetermine a predicted sensed event interval between each consecutivepair of the predicted sensed events, predict that an arrhythmia isdetected or not detected based on the predicted sensed event intervals;and generate an output of data corresponding to the arrhythmia detectionprediction associated with the second setting of the sensing controlparameter. The display unit is configured to receive the generatedoutput of data from the processor and display a visual representation ofthe arrhythmia detection prediction.

This summary is intended to provide an overview of the subject matterdescribed in this disclosure. It is not intended to provide an exclusiveor exhaustive explanation of the apparatus and methods described indetail within the accompanying drawings and description below. Furtherdetails of one or more examples are set forth in the accompanyingdrawings and the description below.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are conceptual diagrams of an ICD system configured tosense cardiac electrical events and deliver cardiac electricalstimulation therapies according to one example.

FIGS. 2A-2C are conceptual diagrams of a patient implanted with the ICDsystem shown in FIGS. 1A-1B in a different implant configuration.

FIG. 3 is a conceptual diagram of an ICD system including transvenousmedical electrical leads according to one example.

FIG. 4 is a conceptual diagram of an intracardiac medical deviceaccording to one example.

FIG. 5 is a conceptual diagram of a medical device configuration forsensing cardiac signals and determining sensed cardiac event dataaccording to one example.

FIG. 6 is a conceptual diagram of circuitry that may be included in thesensing circuit of FIG. 5 according to one example.

FIG. 7 is a flow chart of a method that may be performed by a medicaldevice for sensing cardiac events from a cardiac signal according to oneexample.

FIG. 8 is a diagram of a filtered and rectified cardiac electricalsignal.

FIG. 9 is a diagram of a filtered rectified cardiac electrical signalduring ventricular fibrillation.

FIG. 10 is a flow chart of a method performed by a medical devicesystem, such as the system of FIG. 1A, according to one example.

FIG. 11 is a flow chart of a method for evaluating alternative sensingcontrol parameter settings by a medical device system according toanother example.

FIG. 12 is a table of sensed cardiac event data and classifications ofpredicted sensed and predicted undersensed events of the sensed cardiacevent data according to one example.

FIG. 13 is a diagram of data that may be generated by a processor anddisplayed by display unit according to one example.

FIG. 14 is a diagram of another example of a data table that may bedisplayed by a display unit from data generated by a processor of amedical device system according to techniques disclosed herein.

FIG. 15 is a diagram of a graphical user interface (GUI) that may begenerated as output for display on a display unit according to oneexample.

FIG. 16 is a diagram of a GUI including data generated by a processorfrom a sensing control parameter analysis of sensed cardiac event dataaccording to another example.

FIG. 17 is a diagram of a GUI including a visual representation of datagenerated by a processor according to another example.

FIG. 18 is a diagram of a GUI including a visual representation of datagenerated by a processor according to yet another example.

FIG. 19 is a diagram of a GUI including a visual representation of datagenerated by a processor according to yet another example.

DETAILED DESCRIPTION

In general, this disclosure describes a medical device system andtechniques for determining a rate of cardiac event signals sensedaccording to different settings of at least one sensing controlparameter. Cardiac event signals, also referred to herein as “cardiacevents,” may be sensed by a medical device for determining a cardiacrate and for detecting an abnormal cardiac rhythm for providing cardiacelectrical stimulation therapy as needed. The “cardiac event” beingsensed is an event associated with a single cardiac cycle or heartbeatsuch as an R-wave attendant to ventricular depolarization or a P-waveattendant to atrial depolarization. The cardiac event may be a systolicevent or diastolic event. The cardiac events may be sensed for detectingcardiac arrhythmias. For example, the rate of sensed cardiac events maybe determined for detecting atrial or ventricular tachyarrhythmia, suchas atrial tachycardia (AT), atrial fibrillation (AF), ventriculartachycardia (VT) or ventricular fibrillation (VF). In other examples,the rate of sensed cardiac events may be determined for controllingcardiac pacing for treating bradycardia, asystole or other abnormalrhythms or conduction abnormalities. In some examples, one or morealternative settings of the sensitivity used for sensing cardiac eventsare applied by a processor to sensed cardiac event data to determinewhich sensed cardiac events are still likely to be sensed if thesensitivity is reprogrammed to an alternative setting.

The sensed cardiac event data is determined by a medical device fromcardiac events that are sensed using a programmed sensitivity setting.Using the stored sensed cardiac event data, a processor may determinenew sensed event intervals according to predicted sensed or undersensedevents. This determination of new cardiac event rates or intervalsaccording to an alternative sensitivity setting may be used to determinea time of arrhythmia detection and/or therapy delivery. For example,this determination may be used to determine a time required to detect atachyarrhythmia episode. The techniques disclosed herein for analyzingthe rate and/or intervals of cardiac events according to differentsensing control parameter settings may be implemented in a variety ofcardiac devices configured for sensing cardiac events and determining acardiac event interval or rate for detecting a cardiac rhythm and, insome cases, controlling a cardiac electrical stimulation therapy.

In the illustrative examples presented herein, a cardiac medical device,such as a cardiac monitor, pacemaker or ICD, is configured to sensecardiac electrical signals and deliver cardiac electrical stimulationpulses for capturing and depolarizing the myocardium. The pacemaker orICD may be coupled to a transvenous or non-transvenous lead, or themedical device may be a leadless device in various examples. Forexample, the pacemaker or ICD may be coupled to an“extra-cardiovascular” lead, referring to a lead that positionselectrodes outside the blood vessels, heart, and pericardium surroundingthe heart of a patient. Implantable electrodes carried byextra-cardiovascular leads, for example, may be positionedextra-thoracically (outside the ribcage and sternum) orintra-thoracically (beneath the ribcage or sternum, sometimes referredto as a sub-sternal position) but may not necessarily be in intimatecontact with myocardial tissue. In the examples described below inconjunction with FIGS. 1A-2C, electrodes for sensing cardiac electricalsignals are carried by a lead that may be advanced to asupra-diaphragmatic position, which may be within the thoracic cavity oroutside the thorax in various examples.

In other examples, the medical device may be coupled to a transvenouslead that positions electrodes within a blood vessel but may remainoutside the heart in an “extra-cardiac” location. For example, atransvenous medical lead may be advanced along a venous pathway toposition electrodes within the internal thoracic vein (ITV), anintercostal vein, the superior epigastric vein, or the azygos,hemiazygos, or accessory hemiazygos veins, as examples. In still otherexamples, a transvenous lead may be advanced to position electrodeswithin the heart, such as the intracardiac electrodes generally shown inFIG. 3. Furthermore, a leadless medical device that is located withinthe heart, as generally shown in FIG. 4, or implanted outside the heartfor sensing cardiac electrical signals using electrodes on the housingof the medical device may implement techniques disclosed herein.

More generally, the disclosed techniques may be used in any device thatis configured to determine a rate or intervals of sensed cardiac events,which may include external heart rate monitors such as fitness trackers,watches, or other cardiac monitors that may use skin or surfaceelectrodes for sensing cardiac electrical signals. The techniquesdisclosed herein are not dependent on the particular type of sensingelectrodes used or their position, either internal or external. Themedical devices shown in FIGS. 1A-4 are intended to show illustrativeexamples of devices that may be implemented in a system performingtechniques disclosed herein with no limitation intended.

The cardiac events sensed by any of the devices described herein, e.g.,in conjunction with FIGS. 1A-4 below, are primarily referred to as beingcardiac electrical event signals, which may include P-waves attendant toatrial depolarization, R-waves attendant to ventricular depolarizationor T-waves attendant to ventricular repolarization. However, it is to beunderstood that a cardiac medical device may sense other cardiac signalsthat are not necessarily electrical signals, such as mechanical cardiacsignals. Examples of other types of cardiac signals that may be sensedby an implantable or external medical device include blood pressuresignals, heart sounds, blood flow signals, impedance signals, heartacceleration signals, and oxygen saturation signals. The techniquesdisclosed herein for sensing a cardiac event using a sensing controlparameter setting, storing a cardiac event feature and sensed eventinterval for each sensed cardiac event, and determining which of thesensed cardiac events would be sensed using a different sensing controlparameter setting based on an analysis of the stored sensed eventfeatures and time intervals may be implemented in conjunction with avariety of cardiac signals, not necessarily limited to cardiacelectrical signals.

The terms “cardiac event” and “cardiac event signal” as used hereintherefore refer to any cardiac event that may be sensed during a singlecardiac cycle or heartbeat and is not necessarily an electrical signal.For example, a systolic blood pressure, a diastolic blood pressure, anS1 heart sound, an S2 heart sound, a peak systolic flow, a peak oxygensaturation, and a peak ventricular acceleration, may all be examples ofelectrical or mechanical cardiac event signals that occur on a cyclicalbasis with each cardiac cycle. Cardiac events may be sensed for eachcardiac cycle, e.g., beat-to-beat, over multiple cardiac cycles, todetermine multiple sensed cardiac event intervals, which correspond tothe heart rate. A cardiac rhythm, such as normal sinus rhythm,tachyarrhythmia, bradycardia or other rhythms may be determined frommultiple cardiac event signals occurring at sensed event intervals thatfall into a heart rate zone defining the particular rhythm. Depending onthe sensed cardiac event interval between two consecutively sensedcardiac events, the event ending the sensed cardiac event interval maybe classified as a normal sinus rhythm beat, a premature beat, atachyarrhythmia beat, a bradycardia beat, a ventricular pause, etc.However, in order to detect an arrhythmia, such as atrial or ventriculartachycardia or fibrillation, a threshold number of sensed eventintervals that fall within a tachycardia or fibrillation rate zone maybe required before detection is made and a subsequent therapy isdelivered. Accordingly, the sensing control parameter setting forsensing a single cardiac event signal refers to a setting used to sensea cardiac event that occurs within one cardiac cycle, such as any of theexamples given above. Tachyarrhythmia detection parameters refer toparameters that are applied to detect the heart rhythm over multiplecardiac cycles, based on sensed cardiac events that are each sensedwithin one of the multiple cardiac cycles.

FIGS. 1A and 1B are conceptual diagrams of an ICD system 10 configuredto sense cardiac electrical events and deliver cardiac electricalstimulation therapies according to one example. ICD system 10 is oneexample of a medical device configured sense cardiac electrical signalsand perform the techniques disclosed herein. ICD system 10 includes anICD 14 connected to an extra-cardiovascular electrical stimulation andsensing lead 16. FIG. 1A is a front view of ICD 14 implanted withinpatient 12. FIG. 1B is a side view of ICD 14 implanted within patient12. FIGS. 1A and 1B are described in the context of an ICD system 10capable of providing high voltage CV/DF shocks and in some examplescardiac pacing pulses.

ICD 14 includes a housing 15 that forms a hermetic seal that protectsinternal components of ICD 14. The housing 15 of ICD 14 may be formed ofa conductive material, such as titanium or titanium alloy. The housing15 may function as an electrode (sometimes referred to as a “can”electrode). Housing 15 may be used as an active can electrode for use indelivering CV/DF shocks or other high voltage pulses delivered using ahigh voltage therapy circuit. In other examples, housing 15 may beavailable for use in delivering unipolar, low voltage cardiac pacingpulses and/or for sensing cardiac electrical signals in combination withelectrodes carried by lead 16. In other instances, the housing 15 of ICD14 may include a plurality of electrodes on an outer portion of thehousing. The outer portion(s) of the housing 15 functioning as anelectrode(s) may be coated with a material, such as titanium nitride,e.g., for reducing post-stimulation polarization artifact.

ICD 14 includes a connector assembly 17 (also referred to as a connectorblock or header) that includes electrical feedthroughs crossing housing15 to provide electrical connections between conductors extending withinthe lead body 18 of lead 16 and electronic components included withinthe housing 15 of ICD 14. As will be described in further detail herein,housing 15 may house one or more processors, memories, transceivers,cardiac electrical signal sensing circuitry, therapy delivery circuitry,power sources and other components for sensing cardiac electricalsignals, detecting a heart rhythm, and controlling and deliveringelectrical stimulation pulses to treat an abnormal heart rhythm.

Lead 16 is shown in this example as an extra-cardiovascular leadimplanted outside the ribcage and sternum. Lead 16 includes an elongatedlead body 18 having a proximal end 27 that includes a lead connector(not shown) configured to be connected to ICD connector assembly 17 anda distal portion 25 that includes one or more electrodes. In the exampleillustrated in FIGS. 1A and 1B, the distal portion 25 of lead body 18includes defibrillation electrodes 24 and 26 and pace/sense electrodes28 and 30. In some cases, defibrillation electrodes 24 and 26 maytogether form a defibrillation electrode in that they may be configuredto be activated concurrently. Alternatively, defibrillation electrodes24 and 26 may form separate defibrillation electrodes in which case eachof the electrodes 24 and 26 may be activated independently.

Electrodes 24 and 26 (and in some examples housing 15) are referred toherein as defibrillation electrodes because they may be utilized,individually or collectively, for delivering high voltage stimulationtherapy (e.g., cardioversion or defibrillation shocks). Electrodes 24and 26 may be elongated coil electrodes and generally have a relativelyhigh surface area for delivering high voltage electrical stimulationpulses compared to pacing and sensing electrodes 28 and 30. However,electrodes 24 and 26 and housing 15 may also be utilized to providepacing functionality, sensing functionality or both pacing and sensingfunctionality in addition to or instead of high voltage stimulationtherapy. In this sense, the use of the term “defibrillation electrode”herein should not be considered as limiting the electrodes 24 and 26 foruse in only high voltage cardioversion/defibrillation shock therapyapplications. For example, either of electrodes 24 and 26 may be used asa sensing electrode in a sensing vector for sensing cardiac electricalsignals and determining a need for an electrical stimulation therapy.

Electrodes 28 and 30 are relatively smaller surface area electrodeswhich are available for use in sensing electrode vectors for sensingcardiac electrical signals and may be used for delivering relatively lowvoltage pacing pulses in some configurations. Electrodes 28 and 30 arereferred to as pace/sense electrodes because they are generallyconfigured for use in low voltage applications, e.g., used as either acathode or anode for delivery of pacing pulses and/or sensing of cardiacelectrical signals, as opposed to delivering high voltage CV/DF shocks.In some instances, electrodes 28 and 30 may provide only pacingfunctionality, only sensing functionality or both.

ICD 14 may obtain cardiac electrical signals corresponding to electricalactivity of heart 8 via a combination of sensing electrode vectors thatinclude combinations of electrodes 24, 26, 28 and/or 30. In someexamples, housing 15 of ICD 14 is used in combination with one or moreof electrodes 24, 26, 28 and/or 30 in a sensing electrode vector. In theexample illustrated in FIGS. 1A and 1B, electrode 28 is located proximalto defibrillation electrode 24, and electrode 30 is located betweendefibrillation electrodes 24 and 26. One, two or more pace/senseelectrodes may be carried by lead body 18. For instance, a thirdpace/sense electrode may be located distal to defibrillation electrode26 in some examples. Electrodes 28 and 30 are illustrated as ringelectrodes; however, electrodes 28 and 30 may comprise any of a numberof different types of electrodes, including ring electrodes, short coilelectrodes, hemispherical electrodes, directional electrodes, segmentedelectrodes, or the like. Electrodes 28 and 30 may be positioned at otherlocations along lead body 18 and are not limited to the positions shown.In other examples, lead 16 may include fewer or more pace/senseelectrodes and/or defibrillation electrodes than the example shown here.

In the example shown, lead 16 extends subcutaneously or submuscularlyover the ribcage 32 medially from the connector assembly 27 of ICD 14toward a center of the torso of patient 12, e.g., toward xiphoid process20 of patient 12. At a location near xiphoid process 20, lead 16 bendsor turns and extends superiorly, subcutaneously or submuscularly, overthe ribcage and/or sternum, substantially parallel to sternum 22.Although illustrated in FIG. 1A as being offset laterally from andextending substantially parallel to sternum 22, the distal portion 25 oflead 16 may be implanted at other locations, such as over sternum 22,offset to the right or left of sternum 22, angled laterally from sternum22 toward the left or the right, or the like. Alternatively, lead 16 maybe placed along other subcutaneous or submuscular paths. The path ofextra-cardiovascular lead 16 may depend on the location of ICD 14, thearrangement and position of electrodes carried by the lead body 18,and/or other factors. The techniques disclosed herein are not limited toa particular path of lead 16 or final locations of electrodes 24, 26, 28and 30.

Electrical conductors (not illustrated) extend through one or morelumens of the elongated lead body 18 of lead 16 from the lead connectorat the proximal lead end 27 to electrodes 24, 26, 28, and 30 locatedalong the distal portion 25 of the lead body 18. The elongatedelectrical conductors contained within the lead body 18, which may beseparate respective insulated conductors within the lead body 18, areeach electrically coupled with respective defibrillation electrodes 24and 26 and pace/sense electrodes 28 and 30. The respective conductorselectrically couple the electrodes 24, 26, 28, and 30 to circuitry, suchas a therapy delivery circuit and/or a sensing circuit, of ICD 14 viaconnections in the connector assembly 17, including associatedelectrical feedthroughs crossing housing 15. The electrical conductorstransmit therapy from a therapy delivery circuit within ICD 14 to one ormore of defibrillation electrodes 24 and 26 and/or pace/sense electrodes28 and 30 and transmit sensed electrical signals produced by thepatient's heart 8 from one or more of defibrillation electrodes 24 and26 and/or pace/sense electrodes 28 and 30 to the sensing circuit withinICD 14.

The lead body 18 of lead 16 may be formed from a non-conductivematerial, including silicone, polyurethane, fluoropolymers, mixturesthereof, and/or other appropriate materials, and shaped to form one ormore lumens within which the one or more conductors extend. Lead body 18may be tubular or cylindrical in shape. In other examples, the distalportion 25 (or all of) the elongated lead body 18 may have a flat,ribbon or paddle shape. Lead body 18 may be formed having a preformeddistal portion 25 that is generally straight, curving, bending,serpentine, undulating or zig-zagging.

In the example shown, lead body 18 includes a curving distal portion 25having two “C” shaped curves, which together may resemble the Greekletter epsilon, “c.” Defibrillation electrodes 24 and 26 are eachcarried by one of the two respective C-shaped portions of the lead bodydistal portion 25. The two C-shaped curves are seen to extend or curvein the same direction away from a central axis of lead body 18, alongwhich pace/sense electrodes 28 and 30 are positioned. Pace/senseelectrodes 28 and 30 may, in some instances, be approximately alignedwith the central axis of the straight, proximal portion of lead body 18such that mid-points of defibrillation electrodes 24 and 26 arelaterally offset from pace/sense electrodes 28 and 30.

Other examples of extra-cardiovascular leads including one or moredefibrillation electrodes and one or more pacing and sensing electrodescarried by curving, serpentine, undulating or zig-zagging distal portionof the lead body 18 that may be implemented with the techniquesdescribed herein are generally disclosed in U.S. Pat. No. 10/675,478(Marshall, et al.), incorporated herein by reference in its entirety.The techniques disclosed herein are not limited to any particular leadbody design, however. In other examples, lead body 18 is a flexibleelongated lead body without any pre-formed shape, bends or curves.

ICD 14 analyzes the cardiac electrical signals received from one or moresensing electrode vectors to monitor for abnormal rhythms, such asbradycardia, ventricular tachycardia (VT) or ventricular fibrillation(VF). ICD 14 may analyze the heart rate and morphology of the cardiacelectrical signals to monitor for tachyarrhythmia in accordance with anyof a number of tachyarrhythmia detection techniques. ICD 14 generatesand delivers electrical stimulation therapy in response to detecting atachyarrhythmia (e.g., VT or VF) using a therapy delivery electrodevector which may be selected from any of the available electrodes 24,26, 28 30 and/or housing 15. ICD 14 may deliver ATP in response to VTdetection and in some cases may deliver ATP prior to a CV/DF shock orduring high voltage capacitor charging in an attempt to avert the needfor delivering a CV/DF shock. If ATP does not successfully terminate VTor when VF is detected, ICD 14 may deliver one or more CV/DF shocks viaone or both of defibrillation electrodes 24 and 26 and/or housing 15.ICD 14 may deliver the CV/DF shocks using electrodes 24 and 26individually or together as a cathode (or anode) and with the housing 15as an anode (or cathode). ICD 14 may generate and deliver other types ofelectrical stimulation pulses such as post-shock pacing pulses, asystolepacing pulses, or bradycardia pacing pulses using a pacing electrodevector that includes one or more of the electrodes 24, 26, 28, and 30and the housing 15 of ICD 14.

ICD 14 is shown implanted subcutaneously on the left side of patient 12along the ribcage 32. ICD 14 may, in some instances, be implantedbetween the left posterior axillary line and the left anterior axillaryline of patient 12. ICD 14 may, however, be implanted at othersubcutaneous or submuscular locations in patient 12. For example, ICD 14may be implanted in a subcutaneous pocket in the pectoral region. Inthis case, lead 16 may extend subcutaneously or submuscularly from ICD14 toward the manubrium of sternum 22 and bend or turn and extendinferiorly from the manubrium to the desired location subcutaneously orsubmuscularly. In yet another example, ICD 14 may be placed abdominally.Lead 16 may be implanted in other extra-cardiovascular locations aswell. For instance, as described with respect to FIGS. 2A-2C, the distalportion 25 of lead 16 may be implanted underneath the sternum/ribcage inthe substernal space.

An external device 40 is shown in telemetric communication with ICD 14by a communication link 42. External device 40 may include a processor52, memory 53, display 54, user interface 56 and telemetry unit 58.Processor 52 controls external device operations and processes data andsignals received from ICD 14. Display 54, which may include a graphicaluser interface (GUI), displays data and other information to a user forreviewing ICD operation and programmed parameters as well as cardiacelectrical signals retrieved from ICD 14. As described below, processor52 may receive sensed cardiac event data from ICD 14 for performing ananalysis of the sensed cardiac event data based on different sensingcontrol parameter settings. The analysis may generate a predicted sensedcardiac event rate and/or intervals that indicate how the ICD 14 mayrespond to sensed cardiac events when a different sensing controlparameter setting is programmed in ICD 14 for sensing the cardiac eventsignals.

For example, processor 52 may determine predicted sensed cardiac eventintervals for a different sensitivity setting than the programmedsensitivity setting used by ICD 14 for obtaining sensed cardiac eventdata. Based on the predicted sensed cardiac event intervals, processor52 may determine a time interval until a predicted tachyarrhythmiadetection by ICD 14 and generate a display of data related to theanalysis on display unit 54. In one example, ICD 14 is configured todetermine a maximum peak amplitude of multiple cardiac events that aresensed by the sensing circuitry included in ICD 14. The maximum peakamplitudes may be transmitted to external device 40 as sensed cardiacevent data. Based on the maximum peak amplitudes and a differentsensitivity setting than the sensitivity programmed in ICD 14, processor52 may predict which cardiac events would be sensed with the differentsensitivity setting and determine associated cardiac event intervals.

Processor 52 executes instructions stored in memory 53. Processor 52 mayinclude any one or more of a microprocessor, a controller, a digitalsignal processor (DSP), an application specific integrated circuit(ASIC), a field-programmable gate array (FPGA), or equivalent discreteor analog logic circuitry. In some examples, processor 52 may includemultiple components, such as any combination of one or moremicroprocessors, one or more controllers, one or more DSPs, one or moreASICs, or one or more FPGAs, as well as other discrete or integratedlogic circuitry. The functions attributed to processor 52 herein may beembodied as software, firmware, hardware or any combination thereof.

Memory 53 may include any volatile, non-volatile, magnetic, optical, orelectrical media, such as a random access memory (RAM), read-only memory(ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM(EEPROM), flash memory, or any other digital or analog media. Memory 53may be configured to store sensing control parameters and associatedprogrammable settings. Memory 53 may store predicted sensed cardiacevent data determined by processor 52 for use in generating an outputrepresentative of the predicted sensed cardiac events as disclosedherein.

User interface 56 may include a mouse, touch screen, key pad or the liketo enable a user to interact with external device 40 to initiate atelemetry session with ICD 14 for retrieving data from and/ortransmitting data to ICD 14, including programmable parameters forcontrolling cardiac event sensing and therapy delivery. A clinician mayuse user interface 56 to send and receive commands to ICD 14 viaexternal device 40. As described herein, a clinician may use userinterface 56 to specify one or more sensing control parameters.Typically, user interface 56 includes one or more input devices and oneor more output devices, including display unit 54. The input devices ofuser interface 56 may include a communication device such as a networkinterface, keyboard, pointing device, voice responsive system, videocamera, biometric detection/response system, button, sensor, mobiledevice, control pad, microphone, presence-sensitive screen,touch-sensitive screen (which may be included in display unit 54),network, or any other type of device for detecting input from a human ormachine.

The one or more output devices of user interface 56 may include acommunication unit such as a network interface, display, sound card,video graphics adapter card, speaker, presence-sensitive screen, one ormore USB interfaces, video and/or audio output interfaces, or any othertype of device capable of generating tactile, audio, video, or otheroutput. Display unit 54 may function as an input and/or output deviceusing technologies including liquid crystal displays (LCD), quantum dotdisplay, dot matrix displays, light emitting diode (LED) displays,organic light-emitting diode (OLED) displays, cathode ray tube (CRT)displays, e-ink, or monochrome, color, or any other type of displaycapable of generating tactile, audio, and/or visual output. In otherexamples, user interface 56 may produce an output to a user in anotherfashion, such as via a sound card, video graphics adapter card, speaker,presence-sensitive screen, touch-sensitive screen, one or more USBinterfaces, video and/or audio output interfaces, or any other type ofdevice capable of generating tactile, audio, video, or other output. Insome examples, display unit 54 is a presence-sensitive display that mayserve as a user interface device that operates both as one or more inputdevices and one or more output devices.

Telemetry unit 58 includes a transceiver and antenna configured forbidirectional communication with a telemetry circuit included in ICD 14and is configured to operate in conjunction with processor 52 forsending and receiving data relating to ICD functions via communicationlink 42. Communication link 42 may be established between ICD 14 andexternal device 40 using a radio frequency (RF) link such as BLUETOOTH®,Wi-Fi, or Medical Implant Communication Service (MICS) or other RF orcommunication frequency bandwidth or communication protocols. Datastored or acquired by ICD 14, including cardiac signals or associateddata derived therefrom, results of device diagnostics, and histories ofdetected rhythm episodes and delivered therapies, may be retrieved fromICD 14 by external device 40 following an interrogation command.

In particular, external device 40 may retrieve sensed cardiac event datadetermined by ICD 14. For example, as described below, external device40 may retrieve maximum peak amplitude data from ICD 14. The maximumpeak amplitude of each cardiac event sensed by ICD 14 may be determined,e.g., during a detected tachyarrhythmia episode. The maximum peakamplitudes may be used by processor 52 in an analysis to determinepredicted sensed cardiac event intervals based on a differentsensitivity setting applied to the retrieved maximum peak amplitudes. Inthis way, a prediction of whether a tachyarrhythmia would be detectedusing a different sensitivity setting and the predicted time required todetect the tachyarrhythmia may be determined by processor 52 anddisplayed on a GUI by display unit 54.

External device 40 may be embodied as a programmer used in a hospital,clinic or physician's office to retrieve data from ICD 14 and to programoperating parameters and algorithms in ICD 14 for controlling ICDfunctions. External device 40 may alternatively be embodied as a homemonitor or handheld device. External device 40 may be used to programcardiac signal sensing control parameters, cardiac rhythm detectionparameters and therapy control parameters used by ICD 14. While externaldevice 40 is shown only in FIG. 1A, it is to be understood that all orportions of the techniques disclosed herein may be performed by anexternal device, such as device 40, configured to communicate with animplantable or external medical device configured to sense cardiacelectrical signals, including but not limited to any of the ICDs orpacemakers shown in FIGS. 1A-4. Aspects of external device 40 maygenerally correspond to the external programming/monitoring unitdisclosed in U.S. Pat. No. 5,507,782 (Kieval, et al.), herebyincorporated herein by reference in its entirety. An example programmerthat may be configured to perform the techniques disclosed herein is theCARELINK® Programmer, commercially available from Medtronic, Inc.,Minneapolis, Minn., USA.

In some examples, external device 40 includes external ports 55 adaptedfor electrical connection to a cardiac lead carrying electrodes, such aslead 16 so that processor 52 may receive a cardiac electrical signaldirectly for determining sensed cardiac event data according to onesensitivity setting and analyze the sensed cardiac event data accordingto one or more alternative sensitivity settings according to thetechniques disclosed herein.

FIGS. 2A-2C are conceptual diagrams of patient 12 implanted with ICDsystem 10 in a different implant configuration than the arrangementshown in FIGS. 1A-1B. FIG. 2A is a front view of patient 12 implantedwith ICD system 10. FIG. 2B is a side view of patient 12 implanted withICD system 10. FIG. 2C is a transverse view of patient 12 implanted withICD system 10. In this arrangement, lead 16 of system 10 is implanted atleast partially underneath sternum 22 of patient 12. Lead 16 extendssubcutaneously or submuscularly from ICD 14 toward xiphoid process 20and at a location near xiphoid process 20 bends or turns and extendssuperiorly within anterior mediastinum 36 in a substernal position.

Anterior mediastinum 36 may be viewed as being bounded laterally bypleurae 39, posteriorly by pericardium 38, and anteriorly by sternum 22(see FIG. 2C). The distal portion 25 of lead 16 may extend along theposterior side of sternum 22 substantially within the loose connectivetissue and/or substernal musculature of anterior mediastinum 36. A leadimplanted such that the distal portion 25 is substantially withinanterior mediastinum 36, or within a pleural cavity or more generallywithin the thoracic cavity, may be referred to as a “substernal lead.”

In the example illustrated in FIGS. 2A-2C, lead 16 is locatedsubstantially centered under sternum 22. In other instances, however,lead 16 may be implanted such that it is offset laterally from thecenter of sternum 22. In some instances, lead 16 may extend laterallysuch that distal portion 25 of lead 16 is underneath/below the ribcage32 in addition to or instead of sternum 22. In other examples, thedistal portion 25 of lead 16 may be implanted in otherextra-cardiovascular, intra-thoracic locations, including the pleuralcavity or around the perimeter of and adjacent or within the pericardium38 of heart 8.

FIG. 3 is a conceptual diagram of an ICD system 100 according to anotherexample. ICD system 100 includes ICD 114 coupled to transvenous leads116 and 118 in communication with the right atrium (RA) and rightventricle (RV), respectively, of heart 8. ICD 114 includes a housing 115enclosing circuitry, such as a processor, telemetry circuitry, sensingcircuitry and therapy delivery circuitry, e.g., as generally describedbelow in conjunction with FIG. 5. ICD 114 includes connector assembly117 having connector bores for receiving proximal connectors of RA lead116 and RV lead 118. RA lead 116 may carry a distal tip electrode 120and ring electrode 122 for sensing atrial electrical signals andproducing an atrial intra-cardiac electrogram (EGM) signal. RAelectrodes 120 and 122 may be used for delivering RA pacing pulses. RVlead 118 may carry pacing and sensing electrodes 132 and 134 for sensinga ventricular electrical signal and producing an RV EGM signal. RVelectrodes 132 and 134 may be used to deliver RV pacing pulses. RV lead118 may also carry an RV defibrillation electrode 124 and a superiorvena cava (SVC) defibrillation electrode 126. Defibrillation electrodes124 and 126 are shown as coil electrodes spaced apart proximally fromthe distal pacing and sensing electrodes 132 and 134.

ICD 114 may be configured to provide dual chamber sensing and pacingtherapies as well as high voltage CV/DF shock therapies in response todetecting VT or VF. In other examples, ICD 114 may be configured toprovide multi-chamber sensing and pacing therapies, including CRT, inwhich case a coronary sinus lead may be advanced along a cardiac vein toposition electrodes for sensing and pacing the left ventricle of heart8.

FIG. 4 is a conceptual diagram of an intracardiac pacemaker 214configured to sense cardiac signals and deliver a pacing therapyaccording to another example. Pacemaker 214 may be a transcatheterpacemaker which is adapted for implantation wholly within a heartchamber, e.g., wholly within the right ventricle (RV) or wholly withinthe left ventricle (LV) of heart 8 for sensing cardiac signals anddelivering ventricular pacing pulses. Pacemaker 214 may alternatively beimplantable wholly with an atrial chamber for sensing cardiac signalsand delivering atrial pacing pulses. Pacemaker 214 may be reduced insize compared to subcutaneously implanted pacemakers and may begenerally cylindrical in shape to enable transvenous implantation via adelivery catheter. Pacemaker 214 may include a delivery tool interface218 for engaging with a delivery tool, such as a catheter deliverysystem, for advancing pacemaker 214 along a transvenous pathway and intoheart 8. Pacemaker 214 may include a fixation member 216 for anchoringpacemaker 214 at an implant site within or on heart 8. Pacemaker 214 isshown positioned in the RV, along an endocardial wall, e.g., near the RVapex though other locations are possible. The techniques disclosedherein are not limited to the pacemaker location shown in the example ofFIG. 4 and other positions within or on heart 8 are possible.

Pacemaker 214 may be capable of producing electrical stimulation pulses,e.g., pacing pulses, delivered to heart 8 via one or more electrodes 228and 230 on the outer housing 215 of the pacemaker. For example,pacemaker 214 may be configured to deliver RV pacing pulses and sense anRV cardiac electrical signal using housing based electrodes 228 and 230for producing an RV electrogram (EGM) signal. The cardiac electricalsignals may be sensed using the housing based electrodes that are alsoused to deliver pacing pulses to the RV in some examples.

Pacemaker 214 may include a telemetry circuit for communicating withanother medical device, e.g., external device 40, described above inconjunction with FIG. 1A. In some examples, pacemaker 214 may beconfigured to communicate with another medical device implanted withinthe patient. For example, pacemaker 214 may be co-implanted in a patientimplanted with ICD 14 shown in FIGS. 1A-2C and may be configured tocommunicate with ICD 14 via wireless communication. ICD 14 may, in turn,be configured to communicate with external device 40 and may serve as arelay device for communication between pacemaker 214 and external device40.

Pacemaker 214 may sense cardiac electrical events, e.g., P-waves and/orR-waves, and determine a feature of each sensed event. In some examples,the feature is the maximum peak amplitude of the sensed event. Pacemaker214 may store the maximum peak amplitudes and the sensed event intervalsas cardiac event data for transmission to another medical device foranalysis based on a different sensing control parameter, as describedbelow. External device 40 may generate a display on display unit 54indicating which events sensed by pacemaker 214 would still be sensedusing a different sensing control parameter setting, e.g., a differentsensitivity.

In response to a sensed cardiac event signal, pacemaker 214 may beconfigured to inhibit or trigger a cardiac pacing pulse according to apacing therapy protocol. Pacemaker 214 may schedule a pacing pulse bystarting a pacing interval in response to a sensed cardiac event andgenerate the pacing pulse in response to the pacing interval expiringbefore the next cardiac event signal is sensed. Pacemaker 214 may beconfigured to deliver pacing therapy to provide bradycardia pacing,atrial synchronized ventricular pacing, rate response pacing, asystolepacing or other pacing therapies. In some examples, pacemaker 214 maydetect a tachyarrhythmia based on sensed cardiac event intervals anddeliver ATP therapy in response to detecting the tachyarrhythmia.Pacemaker 214 is described as having pacing capabilities, however, insome examples, the medical device performing techniques disclosed hereinmay be a monitoring only device that senses cardiac event signals anddetermines a feature and interval associated with each sensed cardiacevent for analysis using a different sensing control parameter setting.

FIG. 5 is a conceptual diagram of a medical device configuration forsensing cardiac signals and determining sensed cardiac event dataaccording to one example. FIG. 5 is described in conjunction with theICD 14 of FIGS. 1A-2C for the sake of convenience. It is to beunderstood, however, that the circuitry and functionality attributed tothe circuitry and components described in conjunction with FIG. 5 may beincluded, in whole or in part, in any of the example implantable medicaldevices described or listed herein, such as the ICD 114 shown in FIG. 3or pacemaker 214 shown in FIG. 4. The ICD housing 15 is shownschematically as an electrode in FIG. 5 since the housing of the medicaldevice may be used an electrode for cardiac signal sensing and/ortherapy delivery in some examples. The electronic circuitry enclosedwithin housing 15 includes software, firmware and hardware thatcooperatively monitor cardiac signals, determine when an electricalstimulation therapy is necessary, and deliver therapy as neededaccording to programmed therapy delivery algorithms and controlparameters, which may be stored in memory 82. ICD 14 may be coupled toan extra-cardiovascular lead, such as lead 16 shown in FIG. 1A, carryingextra-cardiovascular electrodes 24, 26, 28, and 30, for deliveringelectrical stimulation pulses to the patient's heart and for sensingcardiac electrical signals. It is understood, however, that electrodes24, 26, 28 and 30 shown in FIG. 5 may be carried by a transvenous leadadvanced within an artery or vein to an extra-cardiac or intracardiaclocation. Furthermore, electrodes coupled to the medical device may behousing based electrodes, on the housing of the medical device as shownin FIG. 4.

ICD 14 as shown in FIG. 5 includes a control circuit 80, memory 82,therapy delivery circuit 84, cardiac electrical signal sensing circuit86, and telemetry circuit 88. In some examples, ICD 14 may include othersensors 94 for sensing a cardiac signal corresponding to any of theexample cardiac signals given above, such as a pressure sensor, flowsensor, impedance sensing circuitry, accelerometer or other motionsensor, optical sensor, acoustical sensor or the like. While sensor(s)94 are conceptually shown enclosed by housing 15 in FIG. 5, it isrecognized that one or more sensors 94 may be enclosed by the medicaldevice housing 15 and/or one or more sensors 94 may be carried outsidethe housing, e.g., on an exterior portion of the housing 15 and/orcarried by a lead extending away from housing 15.

A power source 98 provides power to the circuitry of ICD 14, includingeach of the components 80, 82, 84, 86, 88, and 94 as needed. Powersource 98 may include one or more energy storage devices, such as one ormore rechargeable or non-rechargeable batteries. The connections betweenpower source 98 and each of the other components 80, 82, 84, 86 and 88are to be understood from the general block diagram of FIG. 5 but arenot shown for the sake of clarity. For example, power source 98 may becoupled to one or more charging circuits included in therapy deliverycircuit 84 for charging holding capacitors or other charge storagedevices included in therapy delivery circuit 84 that are discharged atappropriate times under the control of control circuit 80 for producingelectrical pulses according to a therapy protocol. In other examples,power source 98 may serve as a voltage or current source to therapydelivery circuit 84 without requiring a charge storage device. Powersource 98 is also coupled to components of cardiac electrical signalsensing circuit 86, such as sense amplifiers, analog-to-digitalconverters, switching circuitry, etc. as needed.

The circuits shown in FIG. 5 represent functionality included in ICD 14or another medical device operating according to the techniquesdisclosed herein and may include any discrete and/or integratedelectronic circuit components that implement analog and/or digitalcircuits capable of producing the functions attributed to ICD 14 herein.Functionality associated with one or more circuits may be performed byseparate hardware, firmware or software components, or integrated withincommon hardware, firmware or software components. For example, cardiacevent sensing and determination of sensed cardiac event features andsensed event intervals may be performed cooperatively by sensing circuit86 and control circuit 80 and may include operations implemented in aprocessor or other signal processing circuitry included in controlcircuit 80 executing instructions stored in memory 82. Control signalssuch as blanking and timing intervals and sensing threshold amplitudesignals may be sent from control circuit 80 to sensing circuit 86according to programmed sensing control parameter settings.

The various circuits of ICD 14 may include an application specificintegrated circuit (ASIC), an electronic circuit, a processor (shared,dedicated, or group) and memory that execute one or more software orfirmware programs, a combinational logic circuit, state machine, orother suitable components or combinations of components that provide thedescribed functionality. The particular form of software, hardwareand/or firmware employed to implement the functionality disclosed hereinwill be determined primarily by the particular system architectureemployed in the implantable medical device and by the particulardetection and therapy delivery methodologies employed by the implantablemedical device. Providing software, hardware, and/or firmware toaccomplish the described functionality in the context of any modernmedical device, given the disclosure herein, is within the abilities ofone of skill in the art.

Memory 82 may include any volatile, non-volatile, magnetic, orelectrical non-transitory computer readable storage media, such asrandom access memory (RAM), read-only memory (ROM), non-volatile RAM(NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory,or any other memory device. Furthermore, memory 82 may includenon-transitory computer readable media storing instructions that, whenexecuted by one or more processing circuits, cause control circuit 80and/or other ICD components to perform various functions attributed toICD 14 or those ICD components. The non-transitory computer-readablemedia storing the instructions may include any of the media listedabove.

Control circuit 80 communicates, e.g., via a data bus, with therapydelivery circuit 84 and sensing circuit 86 and optionally sensors 94 forsensing cardiac event signals, detecting cardiac rhythms, andcontrolling delivery of cardiac electrical stimulation therapies inresponse to sensed cardiac event signals. Processor 81 may include oneor more digital signal processors (DSPs), general purposemicroprocessors, application specific integrated circuits (ASICs), fieldprogrammable logic arrays (FPLAs), or other equivalent integrated ordiscrete logic circuitry for executing instructions which may be storedin memory 82 to perform functionality attributed to pacemaker 14 herein.

Therapy delivery circuit 84 and sensing circuit 86 are electricallycoupled to electrodes 24, 26, 28, 30, e.g., by lead 16, and the housing15, which may function as a common or ground electrode or as an activecan electrode for delivering CV/DF shock pulses or cardiac pacingpulses. Cardiac electrical signal sensing circuit 86 (also referred toherein as “sensing circuit” 86) may be selectively coupled to electrodes28, 30 and/or housing 15 in order to monitor electrical activity of thepatient's heart. Sensing circuit 86 may additionally or alternatively beselectively coupled to defibrillation electrodes 24 and/or 26 for use ina sensing electrode vector together or in combination with one or moreof electrodes 28, 30 and/or housing 15. Sensing circuit 86 may beenabled to selectively receive cardiac electrical signals from one ormore sensing electrode vectors from the available electrodes 24, 26, 28,30, and housing 15 in some examples. Sensing circuit 86 may monitor oneor more cardiac electrical signals for sensing cardiac electrical eventsand/or producing digitized cardiac signal waveforms for analysis bycontrol circuit 80. For example, sensing circuit 86 may includeswitching circuitry for selecting which of electrodes 24, 26, 28, 30,and housing 15 are coupled to one or more sensing channels of sensingcircuit 86.

As described below in conjunction with FIG. 6, sensing circuit 86 may beconfigured to amplify, filter, rectify and digitize or otherwise processthe cardiac electrical signal received from selected sensing electrodesto improve the signal quality for sensing cardiac electrical eventsignals, such as R-waves or P-waves. Cardiac event detection circuitryincluded within sensing circuit 86 may include one or more senseamplifiers, filters, rectifiers, threshold detectors, comparators,analog-to-digital converters (ADCs), timers or other analog or digitalcomponents configured to sense cardiac electrical events.

Sensing circuit 86 may control an auto-adjusting cardiac event sensingthreshold over each cardiac cycle. Sensing circuit 86 may sense acardiac electrical event in response to a sensing threshold crossing bythe cardiac electrical signal and produce a cardiac sensed event signal,e.g., an atrial sensed event signal in response to a P-wave sensingthreshold crossing or a ventricular sensed event signal in response toan R-wave sensing threshold crossing. The cardiac sensed event signalsare passed to control circuit 80. The cardiac event sensing thresholdmay be set to a starting threshold based on the maximum peak amplitudeof a sensed cardiac event. The cardiac event sensing threshold may decayor decrease from the starting amplitude over the cardiac cycle accordingto one or more decay rates and/or one or more step drops until the nextcardiac event is sensed in response to a sensing threshold crossing. Thecardiac event sensing threshold amplitude may be decreased to a minimumthreshold equal to a programmed sensitivity for sensing the cardiacevent. The programmed sensitivity setting is sometimes referred to asthe “sensing floor” because it is the lowest sensing threshold that maybe reached during a cardiac cycle. The sensing floor may or may not bereached during a given cardiac cycle depending on how early the nextcardiac event signal occurs following the most recently sensed cardiacevent signal.

The sensing threshold amplitude may be decreased from a startingthreshold amplitude toward the programmed sensitivity according to oneor more decay intervals and corresponding decay rates and/or one or moredrop time intervals and corresponding step drops. These sensingthreshold control parameters may be stored in memory 82 and passed tosensing circuit 86 from control circuit 80 for use by hardware, firmwareand/or software of control circuit 80 and/or sensing circuit 86 incontrolling the sensing threshold amplitude.

Control circuit 80 receives the cardiac sensed event signals fromsensing circuit 86 for determining sensed event intervals, e.g., RRintervals (RRIs) and/or PP intervals (PPIs), by timing circuit 90. AnRRI is the time interval between two consecutively sensed R-waves andmay be determined between consecutive ventricular sensed event signalsreceived by control circuit 80 from sensing circuit 86. A PPI is thetime interval between two consecutively sensed P-waves and may bedetermined between consecutive atrial sensed event signals received bycontrol circuit 80 from sensing circuit 86. Timing circuit 90 may startan escape interval timer in response to a sensed event signal andrestart the escape interval timer in response to the next sensed eventsignal. The value of the escape interval timer at the time of the nextsensed event signal may be buffered in memory 82 as the sensed eventinterval for the associated sensed event signal. In this way, memory 82may store a series of sensed event intervals. Each sensed event intervalmay be stored in conjunction with one or more sensed cardiac eventfeatures determined from the sensed cardiac event signal, such as themaximum peak amplitude of the sensed cardiac event signal. As describedbelow in conjunction with FIG. 8, the maximum peak amplitude of a sensedcardiac event may be used to set the starting sensing thresholdamplitude for the next cardiac cycle.

The sensed event signals, e.g., ventricular sensed event signals and/oratrial sensed event signals, may be used by control circuit 80 fordetecting tachyarrhythmia and determining a need for therapy. Forexample, timing circuit 90 may include various timers and/or countersused to control the timing of therapy delivery by therapy deliverycircuit 84. In response to expiration of an escape interval timerwithout receiving a cardiac sensed event signal, control circuit 80 maycontrol therapy delivery circuit 84 to generate and deliver a pacingpulse. Timing circuit 90 may additionally set time windows such asmorphology template windows, morphology analysis windows or performother timing related functions of ICD 14 including synchronizingcardioversion shocks or other therapies delivered by therapy deliverycircuit 84 with sensed cardiac events.

Control circuit 80 may include a tachyarrhythmia detector 92 configuredto analyze signals received from sensing circuit 86 for detectingtachyarrhythmia. Tachyarrhythmia detector 92 may detect tachyarrhythmiabased on cardiac events sensed by sensing circuit 86 meetingtachyarrhythmia detection criteria, such as a threshold number of sensedcardiac events occurring sensed event intervals falling in atachyarrhythmia interval range. Tachyarrhythmia detector 92 may beimplemented in control circuit 80 as hardware, software and/or firmwarethat processes and analyzes signals received from sensing circuit 86 fordetecting tachyarrhythmia, e.g., supraventricular tachycardia (SVT), VTand/or VF. Tachyarrhythmia detector 92 may include comparators andcounters for counting cardiac event intervals, e.g., PPIs or RRIsdetermined by timing circuit 90, that fall into various rate detectionzones for determining an atrial rate and/or a ventricular rate orperforming other rate- or interval-based assessment of cardiac sensedevent signals for detecting and discriminating tachyarrhythmias.

For example, tachyarrhythmia detector 92 may compare the RRIs determinedby timing circuit 90 to one or more tachyarrhythmia detection intervalzones, such as a tachycardia detection interval zone and a fibrillationdetection interval zone. RRIs falling into a detection interval zone arecounted by a respective VT interval counter or VF interval counter andin some cases in a combined VT/VF interval counter included intachyarrhythmia detector 92. The VF detection interval threshold may beset to 300 to 350 milliseconds (ms), as examples. For instance, if theVF detection interval is set to 320 ms, RRIs that are less than 320 msare counted by the VF interval counter. When VT detection is enabled,the VT detection interval may be programmed to be in the range of 350 to420 ms, or 400 ms as an example. RRIs that are less than the VTdetection interval but greater than the VF detection interval may becounted by a VT interval counter. In order to detect VT or VF, therespective VT or VF interval counter is required to reach a threshold“number of intervals to detect” (NID).

As an example, the NID to detect VT may require that the VT intervalcounter reaches 18 VT intervals, 24 VT intervals, 32 VT intervals orother selected NID. In some examples, the VT intervals may be requiredto be consecutive intervals, e.g., 18 out of 18, 24 out of 24, or 32 outof the most recent 32 consecutive RRIs. The NID required to detect VFmay be programmed to a threshold number X VF intervals out of Yconsecutive RRIs. For instance, the NID required to detect VF may be 18VF intervals out of the most recent 24 consecutive RRIs or 30 VFintervals out 40 consecutive RRIs, as examples. When a VT or VF intervalcounter reaches an NID threshold, a ventricular tachyarrhythmia may bedetected by tachyarrhythmia detector 92. The NID may be programmable andrange from as low as 12 to as high as 40, with no limitation intended.VT or VF intervals may be detected consecutively or non-consecutivelyout of the specified number of most recent RRIs. In some cases, acombined VT/VF interval counter may count both VT and VF intervals anddetect a tachyarrhythmia episode based on the fastest intervals detectedwhen a specified NID is reached.

Tachyarrhythmia detector 92 may be configured to perform other signalanalysis for determining if other detection criteria are satisfiedbefore detecting VT or VF, such as R-wave morphology criteria and onsetcriteria. To support additional cardiac signal analyses, sensing circuit86 may pass a digitized electrocardiogram (ECG) signal (or EGM signalwhen sensed using intracardiac electrodes) to control circuit 80 formorphology analysis performed by tachyarrhythmia detector 92 fordetecting and discriminating heart rhythms. A cardiac electrical signalfrom the selected sensing vector may be passed through a filter andamplifier, provided to a multiplexer and thereafter converted to amulti-bit digital signal by an analog-to-digital converter, all includedin sensing circuit 86, for storage in memory 82. Memory 82 may includeone or more circulating buffers to temporarily store digital cardiacelectrical signal segments for analysis performed by control circuit 80.Control circuit 80 may be a microprocessor-based controller includingprocessor 81 that employs digital signal analysis techniques tocharacterize the digitized signals stored in memory 82 to recognize andclassify the patient's heart rhythm employing any of numerous signalprocessing methodologies for analyzing cardiac signals and cardiac eventwaveforms, e.g., R-waves.

Therapy delivery circuit 84 includes charging circuitry, one or morecharge storage devices such as one or more high voltage capacitorsand/or low voltage capacitors, and switching circuitry that controlswhen the capacitor(s) are discharged across a selected pacing electrodevector or CV/DF shock vector. Charging of capacitors to a programmedpulse amplitude and discharging of the capacitors for a programmed pulsewidth may be performed by therapy delivery circuit 84 according tocontrol signals received from control circuit 80. Control circuit 80 mayinclude various timers or counters that control when cardiac pacingpulses are delivered. For example, timing circuit 90 may includeprogrammable digital counters set by a microprocessor of the controlcircuit 80 for controlling the basic pacing time intervals associatedwith various pacing modes or ATP sequences delivered by ICD 14. Themicroprocessor of control circuit 80 may also set the amplitude, pulsewidth, polarity or other characteristics of the cardiac pacing pulses,which may be based on programmed values stored in memory 82.

In response to detecting VT or VF, control circuit 80 may schedule atherapy and control therapy delivery circuit 84 to generate and deliverthe therapy, such as ATP and/or CV/DF therapy. Therapy can be generatedby initiating charging of high voltage capacitors via a chargingcircuit, both included in therapy delivery circuit 84. Charging iscontrolled by control circuit 80 which monitors the voltage on the highvoltage capacitors, which is passed to control circuit 80 via a chargingcontrol line. When the voltage reaches a predetermined value set bycontrol circuit 80, a logic signal is generated on a capacitor full lineand passed to therapy delivery circuit 84, terminating charging. A CV/DFpulse is delivered to the heart under the control of the timing circuit90 by an output circuit of therapy delivery circuit 84 via a controlbus. The output circuit may include an output capacitor through whichthe charged high voltage capacitor is discharged via switchingcircuitry, e. g., an H-bridge, which determines the electrodes used fordelivering the cardioversion or defibrillation pulse and the pulse waveshape.

In some examples, the high voltage therapy circuit configured to deliverCV/DF shock pulses can be controlled by control circuit 80 to deliverpacing pulses, e.g., for delivering ATP, post shock pacing pulses orventricular pacing pulses. In other examples, therapy delivery circuit84 may include a low voltage therapy circuit for generating anddelivering pacing pulses for a variety of pacing needs.

Sensor(s) 94 may include one or more sensors configured to produce acardiac signal having a cyclical or pulsatile waveform corresponding tocardiac events that each occur within a respective cardiac cycle.Sensor(s) 94 may sense a cardiac event, such as a heart sound, systolicblood pressure waveform, impedance waveform, or other pulsatile eventsignal associated with a heartbeat. Sensor(s) 94 may pass cardiac sensedevent signals to control circuit 80 and may determine a sensed cardiacevent feature associated with each sensed event signal. In otherexamples, control circuit 80 may sense cardiac events from a sensorsignal received from sensor(s) 94 and/or determine the event featurefrom the sensor signal in response to a sensed event signal from thesensor. Techniques described herein for sensing cardiac electricalevents, determining sensed event features and sensed event intervals,and analyzing the sensed event features and event intervals based on analternative sensing control parameter setting to predict which cardiacevents in cardiac event data obtained by ICD 14 (or another medicaldevice) will still be sensed may be applied to other cardiac signalssensed by sensor(s) 94.

It is recognized that the methods disclosed herein for determining andanalyzing sensed cardiac event signal features and sensed eventintervals may be implemented in a medical device system that is used formonitoring cardiac electrical signals by sensing circuit 86 and/or othercardiac signals by sensor(s) 94 without necessarily having therapydelivery capabilities or in a pacemaker that monitors cardiac electricalsignals and delivers cardiac pacing therapies by therapy deliverycircuit 84, without high voltage therapy capabilities, such ascardioversion/defibrillation shock capabilities.

Control parameters utilized by control circuit 80 for sensing cardiacevents and controlling therapy delivery may be programmed into memory 82via telemetry circuit 88. Telemetry circuit 88 includes a transceiverand antenna for communicating with external device 40 (shown in FIG. 1A)using RF communication or other communication protocols as describedabove. Under the control of control circuit 80, telemetry circuit 88 mayreceive downlink telemetry from and send uplink telemetry to externaldevice 40. Telemetry circuit 88 may transmit sensed cardiac eventfeatures and associated sensed event intervals to another medical devicefor processing an analysis according to the techniques disclosed herein.In other examples, control circuit 80 may be configured to perform theanalysis of cardiac event signal features and sensed event intervals andcontrol telemetry circuit 88 to transmit the data resulting from and/orused in the analysis.

FIG. 6 is a conceptual diagram of circuitry that may be included insensing circuit 86 according to one example. Sensing circuit 86 iscoupled to a sensing electrode vector, which may include any availableelectrodes selected for sensing cardiac electrical signals and is shownas pace/sense electrodes 28 and 30 as an example. In other examples, thesensing electrode vector coupled to sensing circuit 86 may include adefibrillation electrode 24 and/or 26 and/or housing 15.

The electrical signal developed across the sensing electrode vector,e.g., electrodes 28 and 30, is received as a differential input signalto the pre-filter and pre-amplifier 62. Non-physiological high frequencyand DC signals may be filtered by a low pass or bandpass filter includedin pre-filter and pre-amplifiers 62, and high voltage signals may beremoved by protection diodes included in pre-filter and pre-amplifier62. Pre-filter and pre-amplifier 62 may amplify the pre-filtered signalby a gain of between 10 and 100, and in one example a gain of 17. 5, andmay convert the differential signal to a single-ended output signalpassed to analog-to-digital converter (ADC) 63. Pre-filter and amplifier62 may provide anti-alias filtering and noise reduction prior todigitization.

ADC 63 converts the cardiac electrical signal from an analog signal to adigital bit stream. In one example, ADC 63 may be a sigma-deltaconverter (SDC), but other types of ADCs may be used. In some examples,the output of ADC 63 may be provided to a decimator (not shown), whichfunctions as digital low-pass filter that increases the resolution andreduces the sampling rate of the cardiac electrical signal.

The digital output of ADC 63 may be passed to a digital bandpass filter64. Filter 64 may have a relatively narrow bandpass of approximately 13Hz to 39 Hz for passing cardiac electrical event signals, such asR-waves, typically occurring in this frequency range. In some examples,the digital output of ADC 63 may be passed to a wideband filter 74 havea bandpass of approximately 2.5 to 100 Hz. In some examples, filter 74may include a notch filter to attenuate 60 Hz or 50 Hz line noise.

The narrowband filtered signal is passed from filter 64 to rectifier 65to produce a filtered, rectified signal that is received by a cardiacevent detector 66 for sensing cardiac events in response to thenarrowband filtered and rectified signal crossing a cardiac eventsensing threshold amplitude, for example an R-wave sensing thresholdamplitude. In some examples, cardiac event detector 66 may include aP-wave detector for producing atrial sensed event signals in response toa P-wave sensing threshold and/or a T-wave detector for producing aT-wave sensed event signal in response to a T-wave sensing thresholdcrossing. Cardiac event detector 66 may include an auto-adjusting senseamplifier, comparator and/or other detection circuitry that compares thenarrowband filtered and rectified cardiac electrical signal to a cardiacevent sensing threshold amplitude in real time and produces a sensedevent signal 68, which may be a ventricular sensed (VS) event signal oran atrial sensed (AS) event signal, when the filtered, rectified signalcrosses the cardiac event sensing threshold amplitude outside of anyblanking intervals applied by sensing circuit 86. A cardiac eventsensing threshold applied by cardiac event detector 66 may be amulti-level sensing threshold, for example as generally disclosed incommonly assigned U.S. Pat. No. 10,252,071 (Cao, et al.), incorporatedherein by reference in its entirety.

The rectified signal output from rectifier 65 may be passed to a peakdetector 70, which may include a sample and hold circuit, for detectingthe maximum peak amplitude of the rectified signal following a cardiacsensed event signal 68 produced by cardiac event detector 66. Themaximum peak amplitude may be passed back to cardiac event detector 66for setting the starting cardiac event sensing threshold amplitude forstarting the next cardiac cycle based on the detected maximum peakamplitude of the currently sensed cardiac event. The sensing thresholdamplitude may be set to a starting amplitude that is a percentage of themaximum peak amplitude, e.g., 60%, 70%, 80% or other selectedpercentage. The starting sensing threshold amplitude may be held for atime interval or decay over a decay interval. The sensing thresholdamplitude may be decreased over one or more decay intervals and/or bedecreased by a step drop in amplitude one or more times until it reachesthe minimum sensing threshold amplitude equal to the programmedsensitivity. The techniques described herein are not limited to aspecific behavior of the sensing threshold amplitude as it is decreasedfrom a starting amplitude based on the maximum peak amplitude of themost recently sensed cardiac event signal to a programmed sensitivity.

The maximum peak signal 71 indicates the maximum peak amplitude of thesensed cardiac event signal and is passed to control circuit 80 and/ormemory 82. The maximum peak signal 71 may include a time stampindicating the time of the maximum peak. The maximum peak amplitude andassociated time stamp may be buffered in memory 82. In some examples,the maximum peak amplitude is stored along with a time stamp of thesensed event signal 68 received by control circuit 80 and/or the timestamp of the maximum peak. In this way, a sensed event intervaldetermined by control circuit 80 and the corresponding maximum peakamplitude of the sensed cardiac event (ending the determined sensedevent interval) may be stored in memory 82 in a buffer, which may beconfigured to store a predetermined number of cycles, e.g., on a firstin first out basis. As described below, the maximum peak amplitudes andcorresponding sensed event intervals may be used by control circuit 80or an external processor or computer, e.g., processor 52 of eternaldevice 40 (FIG. 1A), for determining which of the sensed cardiac eventsare predicted to be sensed when an alternative sensitivity setting isused.

The maximum peak amplitude of each sensed event is an event feature thatmay be stored in memory 82 with the corresponding event interval assensed cardiac event data that is analyzed for predicting which of thesensed cardiac events would still be sensed at a different sensitivity(or other programmable sensing control parameter) setting than thecurrently programmed settings used by sensing circuit 86 for sensing thecardiac events. By storing only the cardiac event feature, e.g., maximumpeak amplitude, and the sensed event time interval, control circuit 80or another processor may analyze the sensed cardiac event data topredict the cardiac events that would be sensed using different sensingcontrol parameter settings without requiring storage of the cardiacsignal itself. Storage of the cardiac signal may require significantlyhigher memory capacity which may limit the number of and/or duration ofcardiac signal episodes that may be stored and analyzed. When anothermedical device processor is performing the analysis of the sensedcardiac event data, the data may be transmitted with relatively lesstransmission power and time than required to transmit a stored cardiacsignal episode for analysis by another medical device.

Sensing circuit 86 may include wideband filter 74 for producing acardiac EGM or ECG signal 78 that is passed to control circuit 80 forperforming morphological analysis of the cardiac signal waveforms. Forexample, control circuit 80 may perform morphology analysis of thewideband filtered cardiac electrical signal to detect and distinguishR-waves arising from non-sinus tachycardia or fibrillation waves fromnormally conducted R-waves. While a single sensing electrode vector isshown for passing a signal to both narrowband filter 64 for cardiacevent sensing and wideband filter 74 for morphology signal analysis, inother examples, different sensing electrode vectors may be coupled tosensing circuit 86 for passing different cardiac electrical signals tothe narrowband filter 64 and the wideband filter 74. In some examples,sensing circuit 86 may include two sensing channels including differentfilters, amplifiers, ADCs and/or other signal processing circuitry suchthat two different filtered signals are produced by the respectivesensing channels for use in sensing cardiac event signals and/or formorphology analysis or other signal analyses. The configuration ofsensing circuit 86 as shown in FIG. 6 is illustrative in nature andshould not be considered limiting of the techniques described herein.Sensing circuit 86 may include more or fewer components than illustratedand described in FIG. 6 and some components may be shared betweenmultiple sensing channels.

FIG. 7 is a flow chart 300 of a method that may be performed by amedical device for sensing cardiac events from a cardiac signalaccording to one example. At block 302, sensing circuit 86 may sense acardiac event from a cardiac electrical signal. For example, cardiacevent detector 66 may sense a cardiac event such as a P-wave or R-wavein response to the cardiac signal crossing a sensing threshold. Inresponse to sensing the cardiac event, the cardiac event detector 66 mayproduce a cardiac sensed event signal as described above. At block 304,the sensing circuit 86 (or in some examples control circuit 80) maydetermine an event feature from the sensed cardiac event. In oneexample, the event feature is the maximum peak amplitude of the sensedcardiac event, e.g., the maximum peak P-wave amplitude or the maximumpeak R-wave amplitude, which follows the cardiac sensed event signalduring a post-sense blanking interval. In other examples, the featuredetermined from the sensed event may depend on the criteria used bysensing circuit 86 for sensing the cardiac event. For instance, sensingcircuit 86 may include a slew rate detector for determining the slewrate of the cardiac event signal. An R-wave, for example, may be sensedby the cardiac event detector 66 at block 302 in response to thedetected slew rate exceeding a slew rate threshold. In this case, themaximum slew rate of the cardiac event may be determined as the eventfeature at block 304. Other features of a sensed event that may bedetermined at block 304 may include waveform morphology attributes suchas signal width, signal area, frequency content or the like which may becompared to respective thresholds or ranges for determining if a cardiacevent is sensed. When other event features do not meet cardiac eventsensing criteria, the sensed event according to the sensing thresholdcrossing may be identified as a non-cardiac event. For example, if themorphology of the waveform does not match an R-wave morphology template,the signal width is wider or narrower than an R-wave threshold range, orthe frequency content is above a noise threshold, the sensed event maybe identified as a non-cardiac event and ignored for the purposes ofstoring sensed cardiac event data and/or rejected in the analysis of thesensed cardiac event data according to different sensing controlparameter settings. It is understood that more than one feature may bedetermined from each sensed cardiac event at block 304. In someexamples, cardiac event sensing techniques may rely on one or morecardiac signal features meeting a respective threshold or criterion forsensing the cardiac event, which may include discriminating betweencardiac and non-cardiac (e.g., noise) events. As such, in some examples,multiple features of the sensed cardiac event may be determined at block304.

At block 306, control circuit 80 may determine the sensed event intervalassociated with the currently sensed cardiac event. The sensed eventinterval may be determined by timing circuit 90 as the time intervalfrom the most recent preceding cardiac sensed event signal received fromsensing circuit 86 to the current sensed event signal. The sensed eventinterval and associated maximum peak amplitude (or other determinedfeature) of the current sensed event may be stored in memory 82 at block308 as sensed cardiac event data.

The sensed cardiac event data, including the maximum peak amplitudes(and/or other sensed event features) and the sensed event interval arestored in memory 82 at block 308. In some examples, rather than storingthe sensed cardiac event intervals, a time stamp at the time that acardiac sensed event signal is received, or the time stamp of theassociated maximum peak amplitude, may be stored in memory 82 with thedetermined maximum peak amplitude. The sensed cardiac event data may bestored in memory 82 at block 308 to fill a buffer corresponding to anepisode of the cardiac signal and associated sensed cardiac events. Asdescribed below, the method of flow chart 300 may be performed to obtainsensed cardiac event data during an induced tachyarrhythmia. At othertimes, the method of flow chart 300 may be performed during aspontaneous tachyarrhythmia episode. For example, the process of flowchart 300 may be performed when an increased heart rate is detected bycontrol circuit 80 and the onset of a spontaneous tachyarrhythmiaepisode is suspected due to the increased heart rate. In this way,sensed cardiac event data associated with a spontaneously occurringtachyarrhythmia may be obtained.

In some examples, the data may be determined and buffered in memoryuntil a predetermined number of sensed cardiac event data buffers arefilled, which may be overwritten on a regularly scheduled basis. Inother examples, the sensed cardiac event data may be determined on anongoing basis, filling the sensed cardiac event data buffer on afirst-in-first-out basis. In this way, if control circuit 80 detects atachyarrhythmia or other cardiac arrhythmia episode of interest, thebuffered sensed cardiac event data associated with the arrhythmiaepisode may be saved for analysis according to at least one differentsensing control parameter. In other examples, the sensed cardiac eventdata may be determined over a specified time interval or specifiednumber of sensed cardiac events at scheduled times. The data may beobtained over a time interval that corresponds to cardiac event sensingwith no pacing or cardiac event sensing with intermittent pacing.

In some examples, control circuit 80 may perform subsequent analysis ofthe sensed cardiac event data such that transmission of the data toanother device is not required. In other examples, however, the sensedcardiac event data may be stored in memory 82 for transmission toanother medical device for performing analysis of the data. As such, atblock 310, telemetry circuit 88 may receive a data request from anothermedical device, e.g., external device 40. In response to the datarequest received by telemetry circuit 88, control circuit 80 mayretrieve the stored sensed cardiac event data from memory 82 and controltelemetry circuit 88 to transmit the stored sensed cardiac event data atblock 312. In other examples, telemetry circuit 88 may transmit thesensed cardiac event data without waiting for a data request at block310. For example, when the sensed cardiac event data is acquired duringan induced tachyarrhythmia or other device testing or programmingsession, telemetry circuit 88 may be in communication with the telemetrycircuit of external device 40 and transmit the sensed cardiac event dataas it is acquired or after all data for a cardiac signal episode isacquired.

The data transmitted at block 312 may be analyzed by a processor ofanother device, e.g., external device 40 or a computer receiving datafrom external device 40. As described below, the transmitted sensedcardiac event data may be analyzed according to a setting of aprogrammable sensing control parameter that is different than thesetting currently programmed and used by sensing circuit 86 to sense thecardiac events associated with the transmitted data. By analyzing thesensed cardiac event data according to a different sensing controlparameter setting, the processor may predict which cardiac events willbe sensed according to a different sensing control parameter anddetermine sensed event intervals associated with the predicted sensedevents. The processor may determine a change in a time to detect atachyarrhythmia and/or an expected change in the therapy response of ICD14 when differences in the sensed event intervals exist based on thedifferent sensing control parameter setting. The predicted sensedcardiac events, predicted sensed event intervals, and a predicted timeto detect a tachyarrhythmia may be determined by the processor basedonly the cardiac event data without requiring transmission or storage ofthe cardiac signal from which the actual sensed cardiac event data isobtained.

In the illustrative examples presented herein, a processor of anotherdevice, such as external device 40, a personal computer, a tablet,personal handheld or other device processor may receive the transmittedsensed cardiac event data and perform an analysis of the sensed cardiacevent data based one or more different settings of a programmablesensing control parameter. However, it is recognized that in any of theexamples presented herein, the processor performing the analysis of thesensed cardiac event data may be a processor 81 included in controlcircuit 80. In this case, the sensed cardiac event data need not betransmitted by telemetry circuit 88 but may be stored in memory 82 andretrieved by processor 81 for analysis according to the techniquesdisclosed herein.

FIG. 8 is a diagram of a filtered and rectified cardiac electricalsignal 350 including an R-wave 352, a T-wave 356, and a P-wave 358 andan automatically adjusted R-wave sensing threshold 360 that is adjustedbetween a starting threshold 362 and the programmed sensitivity 370. Thestarting threshold 362 may be determined as a percentage of the maximumpeak amplitude 355 of sensed R-wave 352. R-wave 352 is sensed uponsensing threshold crossing 351. Sensing circuit 86 produces a VS eventsignal 382 in response to the sensing threshold crossing 351. Sensingcircuit 86 may be configured to detect the maximum peak 354 of R-wave352. The maximum peak 354 may be detected during a post-sense blankinginterval 372, e.g., by peak detector 70 shown in FIG. 6. The amplitude355 of the maximum peak 354 may be used by sensing circuit 86 to set thestarting R-wave sensing threshold 362. In some examples, the startingR-wave sensing threshold 362 may be set to a percentage of maximum peakamplitude 355, e.g., between 55% and 70% of the maximum peak amplitude355, or another selected percentage, which may be 62.5% in one example.

The starting threshold 362 may be held for a sense delay interval 374 toavoid oversensing T-wave 356 as an R-wave. In other examples, thestarting threshold 362 may decay at a specified decay rate for apredetermined decay interval. In the example shown, R-wave sensingthreshold 360 is decreased by a step decrement 364 upon expiration ofsense delay interval 374. Sense delay interval 374 may be between 300and 400 ms, as examples, and is 360 ms in one example. At the expirationof sense delay interval 374, sensing circuit 86 adjusts the R-wavesensing threshold 360 from the starting amplitude 362 set to a firstpercentage of maximum peak amplitude 355 to an intermediate sensingthreshold amplitude 366 that is a second percentage of R-wave maximumpeak amplitude 355 that is less than the first percentage. Intermediatesensing threshold amplitude 366 may be set to between 25% and 60% of themaximum peak amplitude 355 or between 30% and 35% of the maximum peakamplitude 355 as examples. Intermediate sensing threshold amplitude 366is less than the starting sensing threshold amplitude 362 by stepdecrement 364.

R-wave sensing threshold 360 may be held at the intermediate amplitude366 for a drop time interval 376 as shown in FIG. 8. In other examples,R-wave sensing threshold 360 may decay at a specified decay rate fromthe expiration of the sense delay interval 374 until the expiration ofdrop time interval 376 or until reaching the sensing floor equal to theprogrammed sensitivity 370. In the example shown, upon expiration ofdrop time interval 376, sensing circuit 86 adjusts R-wave sensingthreshold 360 from the intermediate sensing threshold amplitude 366 tothe sensitivity 370 in a step decrement 368. The sensitivity 370 definesthe minimum sensing threshold amplitude or sensing floor of R-wavesensing threshold 360. The drop time interval 376 may be between 1second and 2 seconds and is 1.5 seconds in one example. The sensitivity370 may be programmable over a range of 0.075 millivolts (mV) to 1.2 mV,as examples, though lower or higher sensitivity settings may beavailable.

Each of the first percentage used to set starting sensing thresholdamplitude 362 as a percentage of maximum peak amplitude 355, the secondpercentage used to set intermediate sensing threshold amplitude 366 as apercentage of maximum peak amplitude 355, the sensitivity 370, thepost-sense blanking interval 372, the sense delay interval 374 and thedrop time interval 376 may be programmable or adjustable sensing controlparameters. Accordingly, processor 52 of external device 40 (and/orcontrol circuit 80) may be configured to analyze sensed cardiac eventdata to determine predicted sensed cardiac events according to one ormore different settings of one sensing control parameter or combinationsof different settings of two or more sensing control parameters. Inillustrative examples described below, control circuit 80 or programmer52 of external device 40 is configured to at least determine predictedsensed cardiac events according to different settings of sensitivity370.

As shown in FIG. 8, R-wave sensing threshold 360 is held at sensitivity370 until the cardiac electrical signal 350 crosses the sensingthreshold 360, at sensing threshold crossing 391, resulting in the nextVS event signal 384 produced by sensing circuit 86. It is to beunderstood that the cardiac electrical signal 350 may not cross thesensing threshold 360 before a pacing interval expires during somecardiac cycles. In this case, therapy delivery circuit 84 may generateand deliver a pacing pulse. At other times, the next R-wave 386 mayoccur earlier after R-wave 352, before R-wave sensing threshold 360reaches sensitivity 370 (before drop time interval 376 expires) or evenbefore R-wave sensing threshold 360 reaches the intermediate sensingthreshold amplitude 366 (before sense delay interval 374 expires). Thecardiac event interval 380, which is an RRI in this example, may bedetermined by control circuit 80 (or processor 52 of external device 40)as the time interval between VS event signal 382 corresponding tothreshold crossing 351 and VS event signal 384 corresponding tothreshold crossing 391.

The maximum peak 383 is identified during the next post-sense blankinginterval 372 and the maximum peak amplitude 385 is determined. Themaximum peak amplitude 385 and the associated RRI 380 may be stored in asensed cardiac event buffer in memory 82 for use in subsequent analysisof alternative sensing control parameters.

It is to be understood that the next R-wave 386 may occur earlier intime after sensed R-wave 352 and cross the sensing threshold 360 beforesensing threshold 360 reaches the minimum sensing threshold 370 duringsome ventricular cycles, particularly during fast ventricular rates. Itis also to be understood that the cardiac electrical signal 350 may notcross the sensing threshold 360 before a pacing interval expires duringsome cardiac cycles. In this case, therapy delivery circuit 84 maygenerate and deliver a pacing pulse. A maximum peak amplitude of anR-wave may not be recorded for a paced cycle. In this case, controlcircuit 80 may store the maximum peak amplitude of the most recentsensed cardiac event or store the average of a predetermined number ofmost recently sensed cardiac events. In this way, a maximum peakamplitude is available for setting the starting sensing threshold 362following a paced event, e.g., at the expiration of a post-pace blankingperiod.

The particular behavior of R-wave sensing threshold 360 shown in FIG. 8as it is adjusted between the starting threshold amplitude 362, setbased on the maximum peak amplitude 355, and the sensitivity 370 is oneillustrative example of how sensing circuit 86 may adjust the sensingthreshold 360. It is to be understood that a variety of cardiac eventsensing threshold control parameters, e.g., R-wave sensing thresholdcontrol parameters for ventricular rate determination or P-wave sensingthreshold control parameters for atrial rate determination, may includeone or more decay rates, each associated with a decay interval, and/orone or more step decrements, each associated with a drop time interval.Various sensing control parameters may be used by sensing circuit 86 foradjusting the R-wave sensing threshold 360 between the startingthreshold 362 and sensitivity 370. For example, the R-wave sensingthreshold 360 may decay, linearly or non-linearly, from starting sensingthreshold amplitude 362 to sensitivity 370 at a predetermined decay rateuntil a sensing threshold crossing or a pacing interval expires,whichever occurs first.

The techniques disclosed herein for determining sensed cardiac eventdata are not limited for use with any particular sensing thresholdcontrol parameters or sensing threshold adjustment schemes. The sensingcontrol parameters used by sensing circuit 86 to adjust sensingthreshold 360, however, are the same sensing control parameters used bycontrol circuit 80 and/or external device processor 52 for determiningpredicted sensed cardiac events during post processing of the sensedcardiac event data. At least one different setting of at least onesensing control parameter is used, however, in determining the predictedsensed cardiac events. For example, one or more sensitivity settingsthat are greater than sensitivity 370 may be applied to determinepredicted sensed cardiac events. In another example, one or more droptime intervals that are longer than drop time interval 376 may beapplied to determine predicted sensed cardiac events. In yet anotherexample, one or more percentages greater than the percentage used to setthe starting sensing threshold 362 and/or the intermediate threshold 366based on a most recent maximum peak amplitude may be applied to thesensed cardiac event data.

Since the sensed cardiac event data obtained by ICD 14 excludes anyundersensed cardiac events, analysis of sensing control parameters thatincrease the sensitivity to sensing cardiac events may be omitted. Forexample, analyzing the sensed cardiac event data using a sensitivitysetting that is lower than sensitivity 370 is not expected to change thesensed event intervals since all cardiac events sensed using thesensitivity 370 are also expected to be sensed at a lower setting of thesensitivity. However, when the setting of sensitivity 370 is increased,effectively reducing the sensitivity to sensing cardiac events, somecardiac events that are sensed using sensitivity 370 may no longer besensed according to a higher sensitivity setting. Likewise, if drop timeinterval 376 is extended to a longer setting and/or the percentage ofmaximum peak amplitude 355 used to set the staring sensing threshold 362and/or the intermediate threshold 366 is higher, the sensitivity tosensing cardiac events may be decreased, resulting in some sensedcardiac events being predicted as undersensed according to thealternative sensing control parameter settings.

The predicted value of the sensing threshold 360 determined by processor52 (or control circuit 80) at the time of a sensed event signal (or itsmaximum peak amplitude) may change from the sensing threshold valueactually applied at the time of a sensed event signal for at least tworeasons. One reason is that the sensing threshold 360 is likely to reachthe minimum sensing threshold earlier in the cardiac cycle when analternative, higher sensitivity setting is being evaluated compared tothe sensing threshold 360 applied according to the programmedsensitivity setting 370. For instance, if the calculated percentage ofthe maximum peak amplitude 355 used to set the starting sensingthreshold 362 or the calculated percentage of the maximum peak amplitude355 used to set the intermediate sensing threshold 366 is less than thealternative sensitivity setting, due to a low amplitude R-wave orfibrillation wave, the predicted sensing threshold is set equal to thesensitivity setting being analyzed instead of the calculated percentage.The sensitivity setting is the sensing floor or minimum sensingthreshold applied to the cardiac signal. Accordingly the predictedsensing threshold at the time of a maximum peak amplitude may be thesensitivity setting under analysis starting from the expiration of thepost-sense blanking period 372 in some instances.

Another reason that the predicted value of the sensing threshold at thetime of a maximum peak amplitude may change from the actual sensingthreshold used to sense the event is that a preceding actual sensedevent may be classified as a predicted undersensed event due to itsmaximum peak amplitude being less than the determined, predicted valueof the sensing threshold corresponding in time to the preceding actualsensed event signal. This situation is described below in conjunctionwith FIG. 9. When an actual sensed event is predicted to be undersensedaccording to an alternative sensitivity setting, the determined sensingthreshold will be decreased according to the maximum peak amplitude ofthe most recent preceding predicted sensed event and the time since thatevent down to the higher, alternative sensitivity setting and held atthe higher sensitivity setting until the next actual sensed event timeafter the classified undersensed event. Assuming the next actual sensedevent is associated with a maximum peak amplitude greater than thehigher sensitivity setting (or other predicted value of the sensingthreshold at the time of the next actual sensed event), the next actualsensed event may be classified by processor 52 as a predicted sensedevent according to the alternative sensitivity setting. The maximum peakamplitude of the classified sensed event is used as a starting value fordetermining the sensing threshold over the next ventricular cycle. Assuch, the predicted behavior of the sensing threshold 360 may bedifferent over one or more cardiac cycles of a cardiac signal episode,resulting in different predicted sensed event intervals between theevents classified as predicted sensed events (and excluding eventsclassified as predicted undersensed events).

FIG. 9 is a diagram 400 of a filtered rectified cardiac electricalsignal 401 during ventricular fibrillation. Signal 401 represents anarrowband rectified signal that may be received by cardiac eventdetector 66 from narrowband filter 64 and rectifier 65. Low amplitudefibrillation waves may be sensed by cardiac event detector 66 accordingto a programmed sensitivity 402. The first fibrillation wave shown has amaximum peak amplitude 420 and is sensed when the cardiac electricalsignal 401 crosses the sensing threshold adjusted to the programmedsensitivity 402. AVS event signal 410 is produced by sensing circuit 86.A post-sense blanking interval 406 is started, and sensing circuit 86determines the maximum peak amplitude 420 during blanking interval 406.

Sensing circuit 86 may determine the starting sensing threshold 408 as apercentage of the maximum peak amplitude 420. Since this startingsensing threshold 408 is less than the programmed sensitivity 402,however, sensing circuit 86 sets the sensing threshold to thesensitivity 402 upon expiration of blanking interval 406. The nextfibrillation wave having maximum peak 421 is sensed when cardiacelectrical signal 401 crosses the sensing threshold set to sensitivity402. Sensing circuit 86 may pass a VS event signal to control circuit80. Because the VS event signal occurs at a sensed event interval 431that is within a VF interval range, control circuit 80 counts a VF event411.

At the programmed sensitivity 402, each fibrillation wave having amaximum peak amplitude 420, 421, 422, 423, 424 and 425 greater than theprogrammed sensitivity 402 is sensed by sensing circuit 80 at respectivesensed event intervals 431, 432, 433, 434 and 435. The starting sensingthresholds indicated by solid black dots, e.g., starting sensingthreshold 408, that are determined by sensing circuit 80 based on therespective maximum amplitudes 420, 421, 422, 423, and 424 are all lessthan the programmed sensitivity 402. As a result the sensing thresholdis set to the sensitivity 402 after each blanking interval 406 until thenext sensing threshold crossing by cardiac electrical signal 401.

One fibrillation wave having maximum peak amplitude 426 is not sensedaccording to the programmed sensitivity 402. As such, the sensingthreshold started after the blanking interval following VF event 413 isheld at the programmed sensitivity 402 until cardiac electrical signal401 crosses the sensing threshold resulting in VS event signal 414. Theassociated sensed event interval 434 is longer than the VF intervalrange so the VS event signal 414 is not counted as a VF event. However,each of the fibrillation waves sensed at a sensed event interval 431,432, 433 and 435 that is within the VF interval range is counted as a VFevent, in this case events 411, 412, 413 and 415. Thus, in the exampleof FIG. 9, four VF intervals would be counted by control circuit 80toward VF detection.

The sensed cardiac event data that may be determined and stored by ICD14 for analysis according to an alternative sensitivity setting 404 mayinclude each of the maximum peak amplitudes 420, 421, 423, 424, and 425of the sensed events along with the respective associated event interval431, 432, 433, 434, and 435 (or a time stamp of the maximum peakamplitude or the sensed cardiac event signal to enable determination ofthe event interval). Since the fibrillation wave having maximumamplitude 426 was not sensed, the maximum peak amplitude 426 is unknownand no sensed cardiac event data is stored corresponding to the unsensedfibrillation wave. The analysis of the sensed cardiac event dataaccording to an alternative sensitivity setting may be performed forsensitivity settings that are higher than the programmed sensitivitysetting 402 since no sensed cardiac event data is available regardinglower amplitude R-waves or fibrillation waves that are smaller inamplitude than the programmed sensitivity.

For the sake of convenience, analysis of the stored maximum peakamplitudes 420, 421, 423, 424, and 425 and associated sensed eventintervals 431, 432, 433, 434 and 435 according to a higher sensitivity404 will now be described as being performed by processor 52 of externaldevice 40. External device 40 may retrieve the cardiac event dataobtained by ICD 14. It is to be understood, however that in someexamples ICD control circuit 80 may perform the analysis of the storedsensed cardiac event data without requiring transmission to the externaldevice 40.

When the alternative higher sensitivity 404 is being applied byprocessor 52 to the sensed cardiac event data, the first maximum peakamplitude 420 is greater than the higher sensitivity 404 and predictedto be a sensed event 450. Processor 52 uses the sensed event timeintervals and associated maximum peak amplitudes of the cardiac eventdata to construct the sensing threshold according to the same sensingcontrol parameters that would be used by cardiac event detector 66, withthe exception of the higher sensitivity 404 in this example. In thisway, processor 52 may determine what value the sensing threshold isadjusted to at the time of each of the stored maximum peak amplitudes.Processor 52 may then determine if a given stored maximum peak amplitudeis greater than or equal to the predicted value of the sensing thresholdat the associated stored sensed event interval. When the stored maximumpeak amplitude is greater than or equal to the predicted value of thesensing threshold, the event is a predicted sensed event. When thestored maximum peak amplitude is less than the predicted value of thesensing threshold, the event is a predicted undersensed event.

In the example of FIG. 9, processor 52 determines a value of thestarting sensing threshold 408 based on the stored maximum peakamplitude 420. Since the starting sensing threshold 408 based on maximumpeak amplitude 420 is less than the higher sensitivity 404, processor 52determines that the predicted value of the sensing threshold at the endof the stored sensed event interval 431 is equal to the highersensitivity 404. Since the maximum peak amplitude 421 stored in thesensed cardiac event data associated with cardiac event interval 431 isless than sensitivity 404, processor 52 classifies the maximum peakamplitude 421 as a predicted undersensed event 451.

The maximum peak amplitude 421 is not used to determine a startingthreshold since it is classified as undersensed. Processor 52 determinesthat the predicted sensing threshold is held at the sensitivity 404until the end of the next stored sensed event interval 432. The maximumpeak amplitude 422 associated with the next stored sensed event interval432 is compared to sensitivity 404. Since maximum peak amplitude 422 isequal to or greater than the sensitivity 404, processor 52 classifiesthe maximum peak amplitude 422 as a predicted sensed event 452. Thisclassification results in a predicted sensed event interval 440associated with the predicted sensed event 452. The predicted sensedevent interval 440 is greater than a VF interval range and is thereforenot determined to be a VF interval by processor 52.

This process of determining the predicted value of the R-wave sensingthreshold at the expiration of each sensed event interval 433, 434 and435 continues with corresponding comparisons of the maximum peakamplitudes 423, 424 and 425 to the predicted sensing threshold value,which is the alternative sensitivity 404 in each of these cases. Themaximum peak amplitude 424 is less than sensitivity 404 (predicted atthe expiration of sensed event interval 434) so a predicted undersensedevent 454 may be made by processor 52. The predicted sensing thresholdis held at sensitivity 404 until the end of the next sensed eventinterval 435 associated with a maximum peak amplitude 425. Processor 52determines that maximum peak amplitude 425 is greater than the predictedvalue of the sensing threshold at sensitivity 404 and determines maximumpeak amplitude 425 as a predicted sensed event 455.

After classifying each of the maximum peak amplitudes 421-425 accordingto the predicted sensing threshold value determined at the expiration ofeach sensed event interval 431-435, respectively, processor 52 maydetermine predicted sensed event intervals 440, 441 and 442 betweenpredicted sensed events 450, 452, 454 and 455. Since two maximum peakamplitudes 451 and 454 are predicted to be undersensed events 451 and454 according to the alternative sensitivity 404, processor 52determines sensed event intervals 440 and 442 that exclude the predictedundersensed events 452 and 454. In this example, only one VF interval441 is predicted according to the alternative, higher sensitivity 404compared to four detected VF intervals 431, 432, 433 and 435 duringsensing according to the programmed sensitivity 402. As described below,processor 52 may determine sensed event intervals according to analternative sensitivity setting to predict a time of tachyarrhythmiadetection and/or therapy delivery according to the alternativesensitivity.

The processor 52 of external device 40 may determine predicted sensedevent intervals based on the classification of the stored maximum peakamplitudes as either undersensed or sensed based on one or morealternative sensitivity settings. The predicted sensed event intervalsmay be used by the processor 52 to determine when an arrhythmiadetection and/or therapy response by ICD 14 is predicted to be differentthan an actual arrhythmia detection and/or therapy response to theactual sensed cardiac events (that are sensed according to theprogrammed sensitivity setting).

FIG. 10 is a flow chart 500 of a method performed by a medical device,such as external device 40 of FIG. 1A, according to one example. Theprocess of flow chart 400 is described as being executed by externaldevice processor 52 for the sake of convenience but may be performed byprocessor 81 of ICD 14 by retrieving sensed cardiac event data frommemory 82 in other examples.

At block 501, processor 52 may obtain sensed cardiac event data from amedical device, e.g., ICD 14. Processor 52 may obtain the sensed cardiacevent data by transmitting an interrogation command to ICD 14 viatelemetry unit 58. Retrieval of the sensed cardiac event data may beinitiated by a user interacting with user interface 56 in some examples.The sensed cardiac event data may correspond to an episode of normalsinus rhythm, bradycardia, tachycardia, fibrillation or other rhythm. Inother examples, as described below, the sensed cardiac event data may bedetermined by ICD 14 during a tachyarrhythmia episode induced during atachyarrhythmia induction procedure and transmitted to external device40. As described in conjunction with FIG. 7, the sensed cardiac eventdata may include the maximum peak amplitude of each cardiac event sensedduring the cardiac rhythm episode and a sensed event time intervalassociated with each maximum peak amplitude.

At block 502, processor 52 determines a starting sensing threshold basedon the first maximum peak amplitude of the sensed cardiac event data.Based on this first starting sensing threshold, the sensed eventinterval associated with the second maximum peak amplitude, and analternative sensitivity setting, processor 52 determines the predictedvalue of the sensing threshold at the expiration of the first sensedevent interval (e.g., interval 431 of FIG. 9) at block 504. At block506, processor 52 compares the predicted sensing threshold to the secondmaximum peak amplitude of the sensed cardiac event data (e.g., peakamplitude 421 of FIG. 9) to classify the second maximum peak amplitudeas a predicted sensed event or a predicted undersensed event accordingto the alternative sensitivity setting. If the second maximum peakamplitude is greater than the predicted value of the sensing threshold,the second maximum peak amplitude is classified as a predicted sensedevent according to the alternative sensitivity setting. If the secondmaximum peak amplitude is less than the determined sensing thresholdvalue, the second maximum peak amplitude is classified as a predictedundersensed event according to the alternative sensitivity setting.

The alternative sensitivity setting may be less sensitive to sensingcardiac events than the sensitivity setting used to obtain the sensedcardiac event data. For example, a sensitivity setting that is greaterthan the programmed sensitivity setting in ICD 14 may be applied forpredicting the value of the sensing threshold. A higher sensitivitysetting corresponds to less sensitivity to sensing cardiac events sincecardiac events having a maximum peak amplitude less than the highersensitivity setting will not be sensed.

Processor 52 may continue the process of determining the predicted valueof the sensing threshold at the end of each sensed event interval andcomparing the predicted value of the sensing threshold to the maximumpeak amplitude associated with the sensed event interval until eachmaximum peak amplitude of the retrieved sensed cardiac event data isclassified at block 506, as determined at block 508. In some examples,processor 52 may compare a second feature of each sensed cardiac event,included in the received sensed cardiac event data, to cardiac eventcriteria at block 506. As described above, when one or more other eventfeatures do not meet cardiac event sensing criteria, the maximum peakamplitude may be associated with a non-cardiac event. For example, if amorphology match score of the sensed cardiac event does not match anR-wave morphology matching threshold, the signal width is wider ornarrower than an R-wave threshold range, or the frequency content isabove a noise threshold, the associated maximum peak amplitude may berejected from the sensed cardiac event data as being a non-cardiac eventin response to at least one second feature of the sensed cardiac eventnot meeting cardiac event criteria. The rejected maximum peak amplitudemay be ignored by processor 52 in classifying each value of the firstfeature as one of a predicted sensed event or a predicted undersensedevent.

When a maximum peak amplitude is classified as a predicted sensed event(“yes” branch of block 510), its maximum peak amplitude is used byprocessor 52 to determine the next starting sensing threshold at block502 for determining the predicted value of the sensing threshold at theend of the next sensed event interval. When a maximum peak amplitude isclassified as an undersensed event (“no” branch of block 510), processor52 determines the sensing threshold at the end of the next sensed eventinterval without determining a starting threshold based on theundersensed maximum peak amplitude. Since a maximum peak amplitudeclassified as undersensed is not predicted to be sensed according to thealternative sensitivity setting, the maximum peak amplitude is not usedin determining a starting sensing threshold. The processor 52 determinesthe predicted value of the sensing threshold at the end of the nextsensed event interval without adjusting the sensing threshold based onthe maximum peak amplitude classified as undersensed. The sensingthreshold is determined according to the sensing threshold controlparameters from the starting sensing threshold based on the most recentmaximum peak amplitude classified as a sensed event until the expirationof the next sensed event interval after the maximum peak amplitudeclassified as an undersensed event. This situation is represented inFIG. 9 by the predicted undersensed event 454. The predicted value ofthe sensing threshold at the expiration of the sensed event interval 435is determined by processor 52 based on any adjustments of the sensingthreshold since the expiration of the post-sense blanking interval 406following the most recent predicted sensed event 453. In this example,the predicted sensing threshold at the expiration of the next sensedevent interval 435 is the higher sensitivity 404.

The maximum peak amplitude associated with the next sensed eventinterval (e.g., maximum peak amplitude 425) is classified by processor52 based on a comparison of the maximum peak amplitude to the predictedvalue of the sensing threshold that ignores any intervening predictedundersensed events. When all maximum peak amplitudes of the sensedcardiac event data have been classified, processor 52 may determine newevent intervals between events classified as predicted sensed events andignore the events classified as predicted undersensed events. As shownin FIG. 9 and described above, an undersensed classification results ina different sensed event interval (e.g., interval 442) than the actualsensed event intervals (e.g., intervals 434 and 435) received from ICD14 in the sensed cardiac event data.

At block 516, processor 52 may determine when an arrhythmia is expectedto be detected based on the predicted sensed event intervals and/orpredict when a therapy is expected to be delivered based on thepredicted sensed event intervals. For example, processor 52 maydetermine a predicted sensed event interval that is longer than aprogrammed pacing lower rate interval and predict delivery of a pacingpulse. As shown in the example of FIG. 9, processor 52 may determine apredicted sensed event interval that is longer than a programmedtachyarrhythmia interval range due to an undersensed eventclassification. When the sensed cardiac event data corresponds to atachyarrhythmia episode, one or more predicted sensed event intervalsthat are longer than tachyarrhythmia event intervals (e.g., VT, VF, ATor AF intervals) stored in the sensed cardiac event data may result in adelay of a tachyarrhythmia detection based on the higher sensitivitysetting (or other sensing control parameter setting) or prevent thetachyarrhythmia detection altogether.

In the example of FIG. 9, only one predicted sensed event interval 441is determined as a VF interval compared to four VF intervals (431, 432,433, and 435) in the sensed cardiac event data. As a result, the highersensitivity 404 may delay or prevent detection of VF. At block 516,processor 52 may count the number of tachyarrhythmia intervals in thepredicted sensed event intervals to determine when tachyarrhythmiadetection criteria are met, if at all, based on the predicted sensedevent intervals. Processor 52 may predict when a tachyarrhythmiadetection is expected (or not) based on the predicted sensed eventintervals and what therapy would be delivered (or not) based on thedetection.

In some examples, the sensed cardiac event data may correspond to a VFepisode and shock delivery. Based on the predicted sensed or undersensedevent classifications according to the alternative sensitivity setting,the predicted sensed event intervals may result in a VT detection andATP therapy delivery, a VF detection that occurs at the same time as theactual VF detection, a VF detection that occurs later than the actual VFdetection such that shock delivery is predicted to occur later than theactual shock delivery, or no VT/VF detection at all and no deliveredtherapy.

At block 518, processor 52 may generate output based on the predictedsensed event intervals and/or arrhythmia detection. In some examples,the output generated at block 518 includes data for display on displayunit 54. The display unit 54 may be a graphical user interface (GUI)that displays a visual representation of the actual sensed cardiac eventdata, the predicted sensed cardiac events, any predicted undersensedcardiac events, the predicted sensed event intervals, a predictedarrhythmia detection and/or therapy response or any combination thereof.The process of FIG. 10 may be performed for multiple alternativesensitivity settings such that data may be displayed for multiplealternative settings. A user may select a sensitivity setting forprogramming into ICD 14 based on the displayed data. Examples of GUIsare described below in conjunction with the accompanying drawings.

In some examples, the output generated at block 518 may include aprogramming command. External device processor 52 may determine arecommended sensing control parameter setting based on the predictedsensed event intervals and/or predicted arrhythmia detection andgenerate a programming command for transmission to ICD 14 by telemetryunit 58. In some instances, processor 52 may determine a sensitivitysetting corresponding to a desired safety margin for detecting atachyarrhythmia. Processor 52 may generate a programming command toadjust the programmed sensitivity stored in ICD memory 82 to theidentified recommended sensitivity setting corresponding to the desiredsafety margin. When the process of flow chart 500 is performed bycontrol circuit 80 of ICD 14, the output at block 518 may includeadjusting the programmed sensitivity setting to a recommended settingdetermined based on the predicted sensed events. The output mayadditionally or alternatively include transmitting analysis results toexternal device 40 for generating a visual representation of theresults.

FIG. 11 is a flow chart 600 of a method for evaluating sensed cardiacevent data according to alternative sensing control parameter settingsby a medical device according to another example. In this example, thesensed cardiac event data determined and stored by ICD 14 is determinedduring an inducted tachyarrhythmia episode. At block 602, ICD 14 mayreceive a VF induction command from external device 40 to inducetachyarrhythmia, e.g., by delivering a T-wave shock or a high frequency(e.g., 50 Hz) burst of pulses. ICD 14 senses ventricular events, e.g.,R-waves and fibrillation waves, during the induced tachyarrhythmia atblock 604 according to the programmed sensitivity and other programmedsensing control parameters. For each sensed event signal produced bysensing circuit 86, ICD 14 determines the maximum peak amplitude and thesensed event interval (or a time stamp associated with the maximum peakamplitude or the sensed cardiac event signal) to store in memory 82 assensed cardiac event data at block 604.

Control circuit 80 detects the induced tachyarrhythmia, e.g., VF, anddelivers therapy, e.g., a shock therapy, according to programmed therapydelivery parameters at block 606. During the induction, detection andtherapy delivery, ICD 14 may be transmitting a wideband filtered EGMsignal, sensed event markers and event intervals, time of detection andtime of a delivered therapy.

At block 608, the sensed cardiac event data including maximum peakamplitudes of sensed events and associated sensed event intervals aretransmitted to external device 40. At block 610, processor 52 classifieseach of the maximum peak amplitudes of the sensed cardiac event data asa predicted undersensed or sensed event based on one or more alternativesensitivity settings, e.g., using any techniques described above inconjunction with FIGS. 9 and 10. At block 612, processor 52 determinespredicted sensed event intervals based on the undersensed and sensedevent classifications. Using the predicted sensed event intervals,processor 52 determines a predicted tachyarrhythmia detection time atblock 614 for each sensitivity setting evaluated.

Processor 52 may generate an output at block 616 based on the predictedtachyarrhythmia detection times determined at block 614. The generatedoutput may include data generated for display by display unit 54, e.g.,in a GUI, which may include a visual representation of a comparisonbetween the actual VF detection time and the predicted detection timefor each of the alternative sensitivity settings evaluated. Processor 52may be configured to determine a safety margin for detectingtachyarrhythmia for one or more sensitivity settings at block 616 asgenerated output. Methods for determining a safety margin are describedbelow in conjunction with FIG. 14. The safety margin may be determinedas the factor of the highest sensitivity setting for whichtachyarrhythmia detection is predicted divided by a given, lowersensitivity margin. For example, if VF detection is predicted at 0.9 mVsensitivity and not predicted at sensitivity settings higher than 0.9mV, the sensitivity setting of 0.45 mV is a predicted 2× safety marginfor detecting VF. The sensitivity setting of 0.3 mV is a predicted 3×safety margin for detecting VF and so on.

In some examples, the generated output may include acceptable orrecommended sensitivity setting(s) for display on the GUI. In stillother examples, the generated output may include a programming commandtransmitted by external device telemetry unit 58 to program arecommended sensitivity setting for use by sensing circuit 86 in sensingcardiac events.

FIG. 12 is a table 650 of sensed cardiac event data and classificationsof predicted sensed and predicted undersensed events of the sensedcardiac event data. Any portion of or all of data listed in table 650may be generated by processor 52 for display by display unit 54, e.g.,in a GUI, in some examples. The data presented in FIG. 12 includessensed cardiac event data received from ICD 14 and predicted sensedevent data determined by an analysis of the sensed cardiac event data.For the sake of convenience, predicted sensed event data presented inFIG. 12 is described as being determined and output by processor 52 ofexternal device 40. As indicated above, however, the predicted sensedevent data may be determined by ICD processor 81 and may be transmittedto external device 40 for generating a visual representation of the datain some examples. In still other examples, the ICD processor 81 and theexternal device processor 52 may cooperatively determine the predictedsensed event data in a distributed manner.

In the first column 652, the sensed cardiac events are numbered andlabeled as VF events in this example. The sensed cardiac events of thesensed cardiac event data may be numbered and labeled according to theassociated sensed event interval, shown in column 653 as the RRI inmilliseconds. For example, the event may be labeled a VS event intervalwhen the sensed event interval is greater than any tachyarrhythmiadetection intervals, a VT interval when the sensed event interval fallsinto a VT interval range, or a VF interval when the sensed eventinterval falls into a VF interval range. In this example, all RRIslisted in column 653 are less than a programmed VF detection interval,e.g., 320 ms, and identified as VF events in column 652.

The maximum peak amplitude of each of the sensed cardiac events islisted in column 656. The programmed sensitivity used by ICD 14 forsensing the listed sensed cardiac events is indicated in cell 654. Inthis example, the programmed sensitivity is 0.075 mV, which may be thelowest available sensitivity setting. In the example of flow chart 600of FIG. 11, external device 40 (or control circuit 80) may temporarilyprogram the sensitivity of ICD sensing circuit 86 to the lowestavailable setting during the tachyarrhythmia induction procedure. Inthis way, the sensed cardiac event data will include all cardiac eventssensed at the lowest available setting (which is the highest sensitivityfor sensing cardiac events). The sensed cardiac event data can beevaluated by external device processor 52 according to all of thealternative sensitivity settings that are higher than the lowestavailable setting.

In the example table 650 of FIG. 12, the alternative, higher sensitivitysettings 660 and 662 of 0.9 mV and 1.2 mV, respectively, are displayedthough it is to be understood that one or more or all of the availablesensitivity settings greater than the programmed sensitivity setting 654may be applied to the sensed cardiac event data in an analysis performedby external device processor 52 or control circuit processor 81. Theclassifications of predicted sensed events (S) and predicted undersensedevents (U) are listed in columns 664 and 666 of table 650 for each ofthe maximum peak amplitudes 656 of the sensed cardiac event data and therespective sensitivity setting 660 or 662.

As described above, external device processor 52 may classify each ofthe maximum peak amplitudes 656 as a predicted sensed event or apredicted undersensed event based on a comparison of the maximum peakamplitude 656 to a sensing threshold predicted according to thealternative sensitivity setting 660 or 662. As described above, thepredicted value of the sensing threshold may be determined by processor52 at the time of the sensed event using the preceding maximum peakamplitude, the sensed event interval and according to the alternativesensitivity setting. The predicted sensing threshold may be compared tothe maximum peak amplitude to classify the maximum peak amplitude as apredicted sensed or undersensed event.

To illustrate, the VF4 event is sensed at an RRI of 242 ms and isdetermined to have a maximum peak amplitude of 1.19 mV. The processor 52may determine the starting sensing threshold based on the precedingmaximum peak amplitude of the VF3 event, which is 1.7 mV. If thepercentage of the maximum peak amplitude used to set the startingthreshold is 62.5%, the starting threshold in this example would be 1.06based on the preceding maximum amplitude. For the alternative testsensitivity 0.9 mV, the sensing threshold is held at the startingsensing threshold of 1.06 for the sense delay interval 362, which may be360 ms according to an example given above. Since the VF4 event issensed at an RRI of 242 ms, the processor 52 determines the predictedsensing threshold at the approximate time of the maximum peak amplitudeas being 1.06 mV for a sensitivity setting of 0.9 mV. Since the maximumpeak amplitude of the VF4 event is 1.19 mV, greater than the predictedsensing threshold of 1.06 mV, the processor 52 determines the VF4 eventas a predicted sensed event for the sensitivity setting of 0.9 mV, asindicated by an “S” in column 664.

Using the same VF4 event as an example for the alternative testsensitivity setting of 1.2 mV 662, the processor 52 determines that thestarting sensing threshold of 1.06 mV based on the preceding maximumpeak amplitude of 1.7 mV is less than the sensitivity setting. As aresult, processor 52 determines the starting sensing threshold to beequal to the sensitivity setting of 1.2 mV since the sensitivity settingis the sensing “floor,” the lowest possible sensing threshold asillustrated in FIG. 8. The starting sensing threshold set to thesensitivity setting of 1.2 mV would be held until a sensing thresholdcrossing occurs. Therefore, at 242 ms after the preceding VF3 event, thepredicted sensing threshold is 1.2 mV. Since the maximum peak amplitudeof the VF4 event is 1.19 mV, less than the predicted sensing threshold,processor 52 determines the VF4 event as a predicted undersensed eventfor the sensitivity setting of 1.2 mV, as indicated by a “U” in column666.

Based on the predicted sensed and undersensed event classifications,processor 52 may determine when a VF detection is predicted according tothe alternative sensitivity settings 660 and 662. As described above,processor 52 may determine predicted sensed event intervals and countthe predicted sensed event intervals that fall into the VF intervalrange. In the example shown in FIG. 12, VF is actually detected when 22VF intervals are detected as indicated at 672. According to sensitivitysetting 0.9 mV 660, the VF5, VF6, VF24 and VF25 events are predictedundersensed events. As a result, a long predicted sensed event intervalis determined from the predicted sensed VF4 event until the nextpredicted sensed VF7 event and from the predicted sensed VF23 event tothe predicted sensed VF26 event. To illustrate, the intervening RRIs ofthe VF5 and VF6 events would be added to the VF7 RRI to determine apredicted RRI of 733 ms for the predicted sensed VF7 event (since themost recent predicted sensed VF4 event). Since the predicted RRI of 733ms is greater than a VT or VF interval, the VF7 event is a predicted VSevent when the sensitivity setting is 0.9 mV. None of the VF5, VF6 andVF7 events, which were each counted as VF events for the actualprogrammed sensitivity setting of 0.075 mV, are counted as VF events byprocessor 52 for the test setting of 0.9 mV.

In some examples, instead of using only an “S” or a “U” to denotepredicted sensed and undersensed events, processor 52 may generate VF,VT, VS or U labels to denote predicted sensed VF events, predictedsensed VT events, predicted sensed VS events and predicted undersensedevents, respectively, based on both the comparison of the predictedsensing threshold to the maximum peak amplitude and the predicted sensedevent interval since the most recent preceding predicted sensed eventcompared to the programmed VT and VF interval ranges. Furthermore, table650 may include predicted sensed event intervals determined by andoutput by processor 52 in addition to an indication of predicted sensedand undersensed events.

In the example of FIG. 12, if the programmed NID to detect VF is set to22 VF intervals, processor 52 may determine that VF is predicted to bedetected upon the VF28 event, at 674, for the 0.9 mV sensitivitysetting. The delay in the predicted VF detection at VF 28 267 from theactual VF detection at the VF22 event 672 results from the longpredicted sensed event intervals from VF4 to VF7 and from VF23 to VF26.Processor 52 may sum all the event intervals from the first predictedsensed VF1 event until the VF28 event meeting VF detection criteria todetermine a predicted VF detection time.

According to sensitivity setting 1.2 mV 662, the VF4, VF5, VF6, VF18,VF19, VF21, VF22, VF24, VF25, VF27, VF28 and VF29 events are predictedundersensed events. Multiple predicted sensed event intervals that arelonger than VT/VF detection intervals, are determined by processor 52from VF3 to VF7, VF17 to VF20, and VF20 to VF26. As a result, processor52 may predict that VF is not detected (ND) 676 when the sensitivitysetting is 1.2 mV based on a count of predicted sensed events occurringat predicted sensed event intervals that are less than the programmed VFdetection interval.

FIG. 13 is a diagram 700 of data that may be generated by processor 52and displayed by display unit 54 of external device 40 according toanother example. In this example, processor 52 may generate a predictedtime to tachyarrhythmia detection 704 (in seconds, s) determined byprocessor 52 based on evaluating sensed cardiac event data according tomultiple sensitivity settings 702 (in millivolts, mV). The programmedsensitivity setting 0.15 mV may be highlighted in the display as shownby dashed box 706. In other examples, the programmed sensitivity settingused to obtain the sensed cardiac event data may be highlighted in thedisplay by enlarged or bolded font, underlining, colored font or otherstylized font or by cell shading or colored fill to distinguish theprogrammed sensitivity setting from sensitivity settings applied to thesensed cardiac event data during the analysis. The data shown in diagram700 may be generated from sensed cardiac event data acquired by ICD 14during a tachyarrhythmia induction, e.g., during a VF induction. Theactual time to detect the VF is 7 seconds when the programmedsensitivity is 0.15 mV in this example.

Since maximum peak amplitude and sensed event interval data is onlyavailable for R-waves and fibrillation waves actually sensed at theprogrammed 0.15 mV sensitivity, predicted sensed events and predictedsensed event intervals need not be determined by processor 52 at lowersensitivities, e.g., 0.075 and 0.1 mV. Any undersensed R-waves orfibrillation waves that occur at the 0.15 mV sensitivity are unknown.Accordingly, processor 52 may generate an assumed time to detect foralternative sensitivity settings that are less than the programmedsensitivity setting. Processor 52 may generate a predicted time todetect VF that is equal to or less than the actual time to detect VF,less than or equal to 7 seconds in this example. Any undersensed eventsat 0.15 mV sensitivity may be sensed at the lower sensitivity settings,potentially resulting in an earlier time to detection. Thus, the time todetect VF is displayed as equal to or less than 7 ms in the example ofFIG. 12.

The time to detect VF at alternative higher sensitivity settings,greater than 0.15 mV in this example, may be estimated by processor 52by determining predicted sensed event intervals based on classifyingeach of the maximum peak amplitudes of the sensed cardiac event data assensed or undersensed events according to each of the alternative highersensitivity settings, e.g., using the techniques described above. In theillustrative example, the time to detect the induced VF is predicted tobe increased from 7 seconds at the programmed sensitivity of 0.15 mV to10 seconds at 0.2 mV sensitivity, 11 seconds at 0.3 mV sensitivity, 12seconds at 0.45 mV and at 0.6 mV sensitivity and 15 seconds at 0.9 mVsensitivity. When the maximum alternative sensitivity setting of 1.2 mVis applied by processor 52 to the sensed cardiac event data, thepredicted sensed event intervals determined by processor 52 do not reachVF detection criteria (e.g., NID not reached) and result in no VFdetection. Based on the displayed data, a user may select a sensitivityto be programmed into ICD 14 which has an acceptable time to detectionbased on the data listed in diagram 700.

FIG. 14 is a diagram 710 of an alternative data table that may bedisplayed by display unit 54 from data generated by processor 52. Inthis example, instead of displaying a time to detection determined byprocessor 52 based on each sensitivity setting 712, processor 52 maygenerate data for display by display unit 54 indicating whether aninduced VF (or other induced or spontaneous tachyarrhythmia) ispredicted to be detected, yes (Y) or no (N), as indicated by column 714,for each available sensitivity setting 712. Processor 52 may determinepredicted sensed event intervals for each of the alternative,sensitivity settings that are higher than the programmed setting, whichmay be the lowest setting of 0.075 mV in this example, and determine ifVF is detected or not based on the predicted sensed event intervals. Aclinician may be most concerned as to whether or not the tachyarrhythmiais detected and less concerned about whether the time to detection isincreased by a few seconds.

In some examples, processor 52 may determine a sensing safety margin 715based on predicted VF detections for display in a GUI on display unit54. The sensing safety margin may be determined as the factor betweenthe highest sensitivity setting at which tachyarrhythmia detection ispredicted to occur and a given sensitivity setting. In the exampleshown, the highest sensitivity setting that VF detection is predicted tooccur is a sensitivity setting of 0.9 mV, which is defined to be a 1×safety margin. At half of the 0.9 mV sensitivity setting, 0.45 mV, thesafety margin for VF detection is 2×. At one-third of the highestsensitivity setting at which VF detection is predicted, 0.3 mV, thesafety margin for detecting VF is 3×. The safety margin for VF detectionis greater than 4× for sensitivity settings of 0.2 mV or less when thehighest sensitivity setting resulting in VF detection is 0.9 mV.

A clinician may desire at least a 2× safety margin or at least a 3 ×safety margin for sensing VF. Accordingly, a visual representation ofthe predicted safety margin for detecting a tachyarrhythmia according topredicted sensed events may be included in a GUI to inform the user ofacceptable sensitivity settings. In the example shown, a 3× safetymargin may be recommended. As such, the sensitivity setting of 0.3 mVcorresponding to a 3 × safety margin may be highlighted in a display ofthe data of diagram 710, e.g., by outlining as shown, bolding,highlighting, colored or other stylized font, shading, colored fill orother formatting.

The data tables shown in FIGS. 13 and 14 may be displayed as part of anoverall GUI that presents a visual representation of sensed cardiacevent data, predicted sensed/undersensed events, and/or predictedarrhythmia detections which may include a corresponding cardiacelectrical signal recording, sensed event markers, sensed eventintervals, tachyarrhythmia detection time, therapy delivered,alternative sensitivity settings (or other sensing threshold controlparameters), predicted sensed event intervals, predicted time ofarrhythmia detections, predicted safety margins, and/or predictedtherapy response.

FIG. 15 is a diagram of a GUI 800 that may be generated based on dataoutput at block 518 of FIG. 10 by external device processor 52 accordingto one example. GUI 800 is displayed on display unit 54. In someexamples, display unit 54 of external device 40 is a touch-sensitivescreen that is configured to both display GUI 800 to a user as well asprovide touch-sensitive regions of GUI 800 that allow the user toprovide input to GUI 800. In other examples, a user may navigate todifferent user input portions of GUI 800, e.g., selectable windows,pop-up-windows, menus, icons, buttons or the like, using a mouse,keyboard or other user interface input device.

GUI 800 may include display of a cardiac electrical signal window 802, atiming diagram window 810, sensed cardiac event data table 820 and ananalysis results window 830. In a cardiac electrical signal window 802of GUI 800, one or more cardiac electrical signals 803 and 804 may bedisplayed. In the example shown, two wideband filtered ECG signalssensed using two different sensing electrode vectors are shown. The twowideband filtered ECG signals may be output from wideband filter 74 ofsensing circuit 86. Signal 803 is labeled Ring1-Ring2 and may correspondto the signal sensed using electrodes 28 and 30 as shown in FIG. 1A.Signal 804 is labeled Coil2-Coil1 and may correspond to the signalsensed using defibrillation electrodes 24 and 26 as shown in FIG. 1A.The sensed cardiac event table 820 includes a listing of sensed cardiacevents (numbered VF1 through VF29) and corresponding maximum peakamplitude of each sensed cardiac event. The data in table 820 representssensed cardiac event data that may be received by external device 40from ICD 14. The data in table 820 may include sensed event intervals,as shown in FIG. 12, in some examples. The sensed cardiac event data oftable 820 represents the maximum amplitude of cardiac events that aresensed by sensing circuit 86 from the narrowband filtered and rectifiedsignal received by cardiac event detector 66. As such, the displayedwideband filtered, non-rectified ECG signals 802 and 804 may notnecessarily be the signal from which the sensed cardiac event data isdetermined but may be the ECG signals output by sensing circuit 86corresponding in time to the narrowband filtered, rectified signal fromwhich the sensed cardiac event data is determined.

The timing diagram window 810 may display additional sensed cardiacevent data by including sensed event intervals 814 determined betweenconsecutive sensed events represented in table 820. The ECG signals 803and 804 may be displayed to enable a clinician to verify the sensedcardiac event data represented in timing diagram window 810. As such,timing diagram window 810 may be aligned in time with the cardiacelectrical signals 803 and 804 to provide a visual representation ofsensed event signals generated by cardiac event detector 66, representedby sense event markers 812, and the corresponding sensed event intervals814 between each consecutive pair of sense event markers 812.

In timing diagram 810, each marker 812 and sensed event interval 814 (inmilliseconds) is generated by processor 52 to indicate the time of acardiac event sensing threshold crossing by the narrowband filtered,rectified signal received by cardiac event detector 86. The sensed eventmarker 812 and sensed event intervals 814 represent the actual sensedcardiac event data received from ICD 14 in this example, however, inother examples, timing diagram window 810 may include multiple rows ofsensed cardiac event markers 812, with each additional row displayingpredicted sensed event makers generated by processor 52 according toalternative sensing control parameter settings, e.g., according todifferent sensitivity settings. Each row of predicted sensed eventmarkers may include corresponding predicted sensed event intervals.

In the example shown, the analysis results window 830 includes abaseline sensitivity 0.075 mV and each available sensitivity setting(0.1 mV through 1.2 mV) greater than the baseline sensitivity. Duringthe VF induction, the programmed sensitivity used by ICD 14 in obtainingsensed cardiac event data may be the lowest sensitivity setting of 0.075mV. The analysis results window 830 includes a visual representation ofpredicted VF detection for each sensitivity setting. The visualrepresentation may include a “yes,” “no,” or “delayed” indicator thatindicates that VF detection is predicted, not predicted, or predictedbut at a later time than the actual VF detection made at the baselinesensitivity. In some examples, the visual representation may include acolor coded cell fill or text indicating acceptable and/or recommendedsensitivity settings and/or unacceptable or non-recommended sensitivitysettings.

For example, the VF detection prediction cells corresponding tosensitivity settings of 0.1 to 0.6 mV may be filled green to indicateacceptable sensitivity settings with predicted VF detection at the sametime (or within an acceptable time limit) of the actual VF detection atthe baseline 0.075 mV sensitivity. A VF detection prediction cellcorresponding to a sensitivity setting (0.9 mV in this example) at whichVF detection is predicted but at a delayed time from the actual VFdetection may be filled yellow to indicate the sensitivity setting is anon-recommended setting. The VF detection prediction cell correspondingto a sensitivity setting (1.2 mV in this example) resulting in nopredicted VF detection may be filled red to indicate an unacceptablesetting. In other examples, the VF detection prediction cells may listthe predicted time to detect and/or a predicted VF detection safetymargin as a visual representation of the predicted performance of ICD 14in detecting VF according to different sensitivity settings. GUI 800 mayinclude a user input region 840. Processor 52 may generate a recommendedsensitivity setting 842 corresponding to a desired VF detection safetymargin 844. A user may select “yes” button 846 to accept and program therecommended sensitivity setting 842 (or “no” button 848 to reject andnot program the recommended setting). In some examples, the recommendedsensitivity setting 842 is a scrollable or drop down menu that enables auser to select different sensitivity settings. Processor 52 maydetermine and adjust the corresponding safety margin 844 displayed for auser selected sensitivity setting 842. Additionally or alternatively,the safety margin 844 may be a scrollable or drop down menu that enablesa user to select different desired safety margins. Processor 52 maydetermine and adjust the displayed sensitivity setting 842 thatcorresponds to a user selected safety margin. The user may select thesensitivity 842 or the safety margin 844 and click on the “yes” button846 to select and program the displayed sensitivity 842 and safetymargin 844. In some examples, when the user clicks the “no” button 848,the processor 52 may generate an alternative recommended sensitivitysetting 842 and corresponding safety margin 844 for display in userinput region 840 to enable the user to accept or reject an alternativesensitivity setting.

The user input region 840 may include a programming pop-up windowdisplayed in response to a user clicking on the “yes” button 846. Thepop-up window may be a programming confirmation window that indicatesthe selected programmable sensitivity setting and include “confirm” and“cancel” user inputs for confirming or cancelling the programming of theselected sensitivity setting in ICD 14. In response to a user inputconfirmation of a sensing control parameter setting, e.g., sensitivitysetting, processor 52 may generate a programming command fortransmission to ICD 14 via telemetry unit 58. While not explicitly shownin GUI 800, other user input portions of GUI 800 may include zoom in andzoom out buttons for viewing cardiac electrical signal window 802 and/ortiming diagram 810 at different horizontal time resolutions and, in thecase of cardiac electrical signal window 802, vertical voltage scaleresolution. Other user input portions of GUI 800 may include a pause,fast forward, reverse, store, download, save, print or other operationalbuttons that enable a user to view, print and/or save data displayed inGUI 800 as desired.

The GUI 800 shown in FIG. 15 illustrates data that may be included in aGUI generated for display by display unit 54. In other examples, GUI 800may include less data or more data than shown in FIG. 15. For example,display of the cardiac electrical signals 803 and 804 may be optional.In some examples, timing diagram 810 is omitted with sensed cardiacevent data presented in table 820, which may include sensed eventintervals for each corresponding maximum peak amplitude. In otherexamples, only table 820 may be shown in GUI 800 or only timing diagram810 may be shown instead of both. GUI 800 may include otherpatient-related data such as a patient name, birthdate or otheridentification (not shown in FIG. 15). GUI 800 may further include otherinformational data such as a display of the date and time that a cardiacelectrical signal episode was recorded by ICD 14 (when transmitted at alater time), therapy delivered, therapy outcome, or the like. GUI 800may include more or fewer user input portions and/or more or fewer datawindows, tables, etc. than shown in FIG. 15.

Accordingly, the techniques set forth herein provide specificimprovements to the computer-related field of programming medicaldevices that have practical applications. For example, the use of thetechniques herein may enable external device 40 to generatevisualizations of sensed cardiac event data, predicted sensed cardiacevents and/or predicted detected arrhythmias, and/or predicted sensedcardiac event interval data corresponding to multiple sensing controlparameter settings that define the cardiac event sensing performed byICD 14. Such visualizations may enable an external device, such asexternal device 40, to inform a user as to how the ICD 14 is expected toperform in sensing cardiac events according to a variety of sensingcontrol parameter settings without requiring ICD 14 to be reprogrammedto perform actual cardiac event sensing and arrhythmia detectionaccording to the variety of sensing control parameter settings.

By providing the GUI 800 or other user interface for displaying the datarelating to predicted sensed cardiac events, the likelihood of humanerror in predicting cardiac event sensing and arrhythmia detectionperformance by ICD 14 and in determining and programming sensing controlparameters is reduced. The displayed data provides a higher confidencein safely programming a higher sensitivity setting than the currentlyprogrammed sensitivity setting based on predicted sensed cardiac eventsand predicted tachyarrhythmia detections. By programming a highersensitivity setting that is associated with a desired safety margin, ICDperformance in detecting arrhythmias with a high degree of sensitivityand specificity is promoted while avoiding false tachyarrhythmiadetections. Furthermore, the techniques disclosed herein may reduce thecomplexity of programming a medical device to sense cardiac events tothe degree of accuracy required for controlling the delivery and timingof cardiac electrical stimulation therapies, e.g., pacing and/or CV/DFtherapies. As such, the techniques disclosed herein may enable a medicaldevice, such as ICD 14, to be programmed to sense cardiac events in amanner that is simplified, flexible, and patient-specific such that theICD may reliably sense cardiac events to control delivery and timing oftherapies.

FIG. 16 is a diagram 850 of a GUI that may be generated for display bydisplay unit 54 including data generated by external device processor 52(or ICD processor 81) from the sensing control parameter analysis ofsensed cardiac event data received from ICD 14 according to anotherexample. In this example, GUI 850 includes a cardiac signal window 852which may display a real time ECG or EGM signal received from animplanted medical device. Alternatively, the displayed cardiac signalmay be a stored cardiac signal episode corresponding in time to thesensed cardiac event data represented by the analysis results presentedin the analysis results window 880. A historical data/information window854 is shown including a history of arrhythmia and/or noise detectionepisodes detected by the ICD 14, e.g., a ventricular oversensing ofnoise detection and a non-sinus VT detection in the example shown, withcorresponding date and time stamps, average and maximum ventricularrates, and an indication of the most recent interrogation session withthe ICD 14.

The analysis results window 880 in this example displays a calculatedtime to detection table representing the actual time to detect atachyarrhythmia 885 for the programmed sensitivity setting 882 and thepredicted time to detect 886 for all other available sensitivitysettings 884. Note that the predicted times to detect for sensitivitysettings less than the programmed sensitivity setting 882 are listed asequal to or less than the actual time to detect 885, since any R-wavesor fibrillation waves undersensed at the programmed sensitivity settingof 0.15 mV (in this example) are unknown and excluded from the sensedcardiac event data.

The predicted times to detect 886 listed for sensitivity settings 884that are higher than the programmed sensitivity setting of 0.15 mV (inthis example) are determined by processor 52 using the techniquesdescribed above. For example, processor 52 may receive the maximum peakamplitude of each sensed cardiac event and an associated time stamp orsensed event interval as sensed cardiac event data from ICD 14.Processor 52 may predict the value of the sensing threshold at eachassociated time stamp or sensed cardiac event interval using the mostrecent preceding maximum peak amplitude and according to sensingthreshold control parameters, e.g., as described in conjunction withFIG. 8, and compare the predicted sensing threshold value to theassociated maximum peak amplitude to classify each maximum peakamplitude as either a predicted sensed event or a predicted undersensedevent.

Processor 52 may determine predicted sensed event intervals between allconsecutive pairs of predicted sensed events and count the predictedsensed event intervals that fall into a tachyarrhythmia interval range.Processor 52 may determine if the count of predicted tachyarrhythmiasensed event intervals reaches an NID and sum the predicted sensedintervals that occur from the first predicted tachyarrhythmia sensedevent interval to and including the last predicted tachyarrhythmiasensed event interval that reaches the NID. This sum of the predictedsensed event intervals may be rounded or truncated and displayed as thetime to detect in analysis results window 880. When the NID is notreached, an indication of “no detection” is displayed, as observed forthe sensitivity setting of 1.2 mV. While not shown explicitly in FIG.16, the analysis results window may include a programming user inputfeature or icon to enable the user to select a desired sensitivitysetting for programming into ICD 14 based on the data displayed, asgenerally described above in conjunction with FIG. 15.

Various user input icons or buttons may also be displayed in GUI 850 asshown allowing a user to interact with the GUI using a touch screen,mouse, or other pointing tool or user interface device, e.g., to selectdifferent screens for display on display unit 54 which may include aprogrammable parameters display, select text or graphical versions ofthe displayed data, print or save displayed data, interrogate ICD 14,end the programming and interrogation session or the like.

FIG. 17 is a diagram 900 of a GUI that may be displayed by display unit54 including data generated by processor 52 according to anotherexample. In this example, the analysis results window 930 includes avertical tabular listing of the available sensitivity settings 934, withthe programmed sensitivity setting 932 corresponding to the actualsensed cardiac event data designated by a “P” icon. Instead of listingthe predicted (or actual) time to detect for each sensitivity setting,predicted VF detections 938 (and the actual VF detection for theprogrammed sensitivity setting) are designated as a “yes” (Y) or a “no”(N). In this example, no VF detection is predicted for the highestsensitivity setting 1.2 mV. In some examples, a clinician may not beconcerned with differences in times to detect and is primarily concernedwith whether or not detection is predicted in selecting sensing controlparameters.

FIG. 18 is a diagram 950 of a GUI that may be generated for display bydisplay unit 54 including predicted sensed event related data generatedby processor 52 according to yet another example. In this example, theanalysis results window 980 includes a table indicating the programmedsensitivity setting 982, a listing of only higher available sensitivitysettings 984 that are greater than the programmed sensitivity setting982, corresponding predicted (and actual) times to VF detection 986 andthe safety margin 985 determined by processor 52 for each sensitivitysetting 984. Available sensitivity settings less than the programmedsensitivity setting may be omitted from the analysis results window 980in some examples since the predicted times to detect are not determinedby processor 52 by way of predicting sensed cardiac events. Thepredicted times to detect for lower sensitivity settings may be assumedand are predicted to be equal to or less than the actual time to detectfor the programmed sensitivity setting.

As described above, processor 52 may determine the safety margin as thefactor of the highest sensitivity at which detection occurs divided by agiven sensitivity setting. The safety margin for the highest sensitivitysetting at which VF detection is predicted is set as 1×. The safetymargin for each lower sensitivity setting may be set to the rounded ortruncated factor of the highest sensitivity setting at which VFdetection is predicted divided by the lower sensitivity setting.

In some examples, the sensitivity settings 984 corresponding to at leasta 2× safety margin may be highlighted as acceptable sensitivitysettings, e.g., by colored, highlighted or other stylized font orformatting. The sensitivity setting corresponding to a recommendedsafety margin, e.g., 3×, may be distinguished from acceptablesensitivity settings by different stylized font or formatting, cellcolor or fill, highlighting, etc. As indicated above, the analysisresults window 980 may include a user input button or region to acceptand enable programming of a recommended sensitivity setting.

FIG. 19 is a diagram 1000 of a GUI that may be generated for display bydisplay unit 54 including predicted sensed event related data generatedby processor 52 according to yet another example. The analysis resultswindow 1030 in this example includes a graph 1032 of the sensing controlparameter analysis results of the sensed cardiac event data instead of atabular or text display as shown in FIGS. 15-17. A user may togglebetween a plotted graphical display and a text or table display of thedata using user input selection buttons 1031 in some examples. When“plot” 1031 is selected, the predicted times to VF detection 1038 may begraphed along the y-axis 1034 for each available sensitivity settingplotted along the x-axis 1036. The actual programmed sensitivity setting1040 may be indicated by a “P” icon with the corresponding actual timeto VF detection 1042. Various formatting techniques may be used tohighlight the programmed and recommended or acceptable and/ornon-recommended or unacceptable sensitivity settings in the graph 1032.For example, all settings resulting in at least a 2× safety margin maybe shown by a green plot symbol. A setting resulting in a desired safetymargin, e.g., 3×, may be displayed as an enlarged plot symbol and/orwith an “R” icon or labeled as 3 × safety margin. All sensitivitysettings resulting in a 1× safety margin may be displayed asnon-recommended settings indicated by a yellow plot symbol and/or an “X”plot symbol instead of a circle “O,” for example. Any sensitivitysetting resulting a prediction of no VF detection may be distinguishedas an unacceptable setting by a red plot symbol and/or an “X” plotsymbol or be shaded or darkened compared to other plotted symbols orleft out altogether to indicate that this setting should not beprogrammed. As generally described above, the analysis results window1030 may include a user input region enabling a user to select asensitivity setting for programming into ICD 14.

While the techniques described herein generally refer to processor 52receiving sensed cardiac event data transmitted from ICD 14, it iscontemplated that processor 52 may determine sensed cardiac event datafrom a received cardiac electrical signal and perform the subsequentanalysis of the sensed cardiac event data according to different sensingcontrol parameter settings. The sensed cardiac event data may bedetermined by processor 52 from a cardiac electrical signal received byexternal device 40 via sensing electrodes coupled to external device 40,e.g., carried by lead 16 and coupled via alligator clips and wires orother electrical connectors. Alternatively, the sensed cardiac eventdata may be determined by processor 52 from a cardiac signal transmittedfrom ICD 14 (or another implantable medical device).

In still other examples, ICD control circuit 80 may perform the sensedcardiac event analysis described herein and transmit data of theanalysis results to external device 40 via telemetry circuit 88.Processor 52 may generate output based on the received data for displayby display unit 54. In some examples, control circuit 80 mayadditionally or alternatively adjust the programmed sensitivity to adifferent setting based on the results of the sensed cardiac event data.As such, a single medical device processor may perform the methodsdisclosed herein for receiving sensed cardiac event data, analyzing thesensed cardiac event data according to at least one different sensingcontrol parameter settings and generating an output, which may include aprogramming command and/or data for display in a GUI.

It should be understood that, depending on the example, certain acts orevents of any of the methods described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of themethod). Moreover, in certain examples, acts or events may be performedconcurrently, e.g., through multi-threaded processing, interruptprocessing, or multiple processors, rather than sequentially. Inaddition, while certain aspects of this disclosure are described asbeing performed by a single circuit or unit for purposes of clarity, itshould be understood that the techniques of this disclosure may beperformed by a combination of units or circuits associated with, forexample, a medical device.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored as one or more instructions orcode on a computer-readable medium and executed by a hardware-basedprocessing unit. Computer-readable media may include computer-readablestorage media, which corresponds to a tangible medium such as datastorage media (e.g., RAM, ROM, EEPROM, flash memory, or any other mediumthat can be used to store desired program code in the form ofinstructions or data structures and that can be accessed by a computer).

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPLAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

Thus, a medical device system has been presented in the foregoingdescription with reference to specific examples. It is to be understoodthat various aspects disclosed herein may be combined in differentcombinations than the specific combinations presented in theaccompanying drawings. It is appreciated that various modifications tothe referenced examples may be made without departing from the scope ofthe disclosure and the following claims.

What is claimed is:
 1. A medical device comprising: a processorconfigured to: receive sensed cardiac event data comprising a value of afirst feature determined from each one of a plurality of cardiac eventssensed from a cardiac signal according to a first setting of a sensingcontrol parameter; classify each value of the first feature of each oneof the plurality of cardiac events as one of a predicted sensed event ora predicted undersensed event according to a second setting of thesensing control parameter, the second setting being less sensitive tosensing cardiac events than the first setting; determine a predictedsensed event interval between each consecutive pair of the predictedsensed events; predict that an arrhythmia is detected or not detectedbased on the predicted sensed event intervals; and generate an outputbased on the arrhythmia detection prediction associated with the secondsetting of the sensing control parameter.
 2. The medical device of claim1, wherein the processor is configured to classify each value of thefirst feature of each one of the plurality of cardiac events by;determining a predicted value of a sensing threshold based on at leastthe first value of the first feature of a preceding one of the pluralityof cardiac events; comparing the value of the first feature to thepredicted value of the sensing threshold; and classifying the value ofthe first feature as a predicted sensed event in response to the valueof the first feature being greater than or equal to the sensingthreshold value.
 3. The medical device of claim 1, wherein the receivedsensed cardiac event data comprises one of a time stamp or a sensedevent interval associated with each value of the first feature of eachone of the plurality of cardiac events wherein the processor isconfigured to classify each value of the first feature by: predicting avalue of a sensing threshold at one of the time stamp or the sensedevent interval associated with the value of the first feature; comparingthe value of the first feature to the predicted value of the sensingthreshold; and classifying the value of the first feature as a predictedsensed event in response to the value of the first feature being greaterthan or equal to the sensing threshold value.
 4. The medical device ofclaim 1, wherein the value of the first feature of each of the pluralityof cardiac events sensed from the cardiac signal according to the firstsetting of the sensing control parameter is a maximum peak amplitude andthe first setting of the sensing control parameter is a firstsensitivity setting, wherein the processor is configured to classifyeach maximum peak amplitude as one of a predicted sensed event or apredicted undersensed event according to the second setting of thesensing control parameter by: determining a sensing threshold valueaccording to the second setting, the second setting being a secondsensitivity setting that is greater than the first sensitivity settingso that the second sensitivity setting is less sensitive to sensingcardiac events than the first sensitivity setting; comparing the maximumpeak amplitude to the sensing threshold value; and classifying themaximum peak amplitude as a predicted sensed event in response to themaximum peak amplitude being greater than or equal to the sensingthreshold value.
 5. The device of claim 1, further comprising: a displayunit; wherein the processor is configured to; predict the arrhythmia isdetected or not detected by: comparing the predicted sensed eventintervals to tachyarrhythmia detection criteria; predicting thearrhythmia is detected by predicting a tachyarrhythmia detection inresponse to the predicted sensed event intervals meeting thetachyarrhythmia detection criteria; and generate the output bygenerating data corresponding to the predicted tachyarrhythmia detectionfor display by the display unit in a graphical user interface.
 6. Themedical device of claim 5, wherein the processor is configured togenerate the output by: determining a predicted time to detect thetachyarrhythmia; and generate the data corresponding to the predictedtachyarrhythmia detection comprising the predicted time to detect thetachyarrhythmia. The medical device of claim 5, wherein the processor isconfigured to: for each setting of a plurality of settings of thesensing control parameter that are less sensitive to sensing cardiacevents than the first setting: classify the value of the first featureof each one of the plurality of cardiac events as one of a predictedsensed event or a predicted undersensed event according to the settingof the plurality of settings; determine a predicted sensed eventinterval between each consecutive pair of the predicted sensed events;and predict that a tachyarrhythmia is detected or not detected based onthe predicted sensed event intervals; and generate the output by:determining a least sensitive setting of the plurality of settingsassociated with a predicted arrhythmia detection; determining a safetymargin for detecting the tachyarrhythmia for each setting of theplurality of settings of the sensing control parameter, by determining afactor of the least sensitive setting associated with the predictedarrhythmia detection divided by the setting of the plurality ofsettings; and generating the data corresponding to the predictedtachyarrhythmia detection comprising the determined safety margins fordisplay by the display unit in the graphical user interface.
 8. Themedical device of claim 7, wherein the plurality of cardiac eventssensed from the cardiac signal according to the first setting of thesensing control parameter correspond to a detected tachyarrhythmia; andthe processor is further configured to: predict a tachyarrhythmiadetection for each programmable setting of the sensing control parameterthat is more sensitive to sensing cardiac events than the first setting;and generate the output by determining a safety margin for display bythe display unit in the graphical user interface for each of theprogrammable settings of the sensing control parameter that is moresensitive to sensing cardiac events than the first setting.
 9. Themedical device of claim 1, further comprising a display unit; whereinthe processor is configured to: for each setting of a plurality ofsettings of the sensing control parameter that are less sensitive tosensing cardiac events than the first setting: classify the value of thefirst feature of each one of the plurality of cardiac events as one of apredicted sensed event or a predicted undersensed event; determine apredicted sensed event interval between each consecutive pair of thepredicted sensed events; and predict that a tachyarrhythmia is detectedor not detected based on the predicted sensed event intervals; andgenerate the output by generating a visual representation of eachsetting of the plurality of settings of the sensing control parameterthat is less sensitive than the first setting and an associatedtachyarrhythmia detection prediction for display by the display unit inthe graphical user interface.
 10. The medical device of claim 1, whereinthe processor is configured to: determine a recommended setting of thesensing control parameter based on the arrhythmia detection predictionassociated with the second setting of the sensing control parameter; andgenerate the output by generating a programming command to adjust thesensing control parameter to the recommended setting.
 11. The medicaldevice of claim 1, wherein the received sensed cardiac event datafurther comprises a second value of a second feature determined fromeach one of the plurality of cardiac events sensed from the cardiacsignal according to the first setting of the sensing control parameter;wherein the processor is configured to: determine that the second valueof the second feature associated with a given one of the plurality ofcardiac events does not meet cardiac event criteria; reject the value ofthe first feature associated with the given one of the plurality ofcardiac events from the sensed cardiac event data as being a non-cardiacevent in response to the second value of the second feature not meetingcardiac event criteria; and ignore the rejected value of the firstfeature in classifying each value of the first feature as one of apredicted sensed event or a predicted undersensed event.
 12. A methodcomprising: receiving sensed cardiac event data comprising a value of afirst feature determined from each one of a plurality of cardiac eventssensed from a cardiac signal according to a first setting of a sensingcontrol parameter; classifying each value of the first feature of eachone of the plurality of cardiac events as one of a predicted sensedevent or a predicted undersensed event according to a second setting ofthe sensing control parameter, the second setting being less sensitiveto sensing cardiac events than the first setting; determining apredicted sensed event interval between each consecutive pair of thepredicted sensed events; predicting that an arrhythmia is detected ornot detected based on the predicted sensed event intervals; andgenerating an output based on the arrhythmia detection predictionassociated with the second setting of the sensing control parameter. 13.The method of claim 12, wherein classifying each value of the firstfeature of each one of the plurality of cardiac events comprises;determining a predicted value of a sensing threshold based on at leastthe value of the first feature of a preceding one of the plurality ofcardiac events; comparing the value of the first feature to thepredicted value of the sensing threshold; and classifying the value ofthe first feature as a predicted sensed event in response to the valueof the first feature being greater than or equal to the sensingthreshold value.
 14. The method of claim 12, wherein the sensed cardiacevent data comprises one of a time stamp or a sensed event intervalassociated with each value of the first feature of each one of theplurality of cardiac events wherein the processor is configured toclassify each value of the first feature by: predicting a value of asensing threshold at one of the time stamp or the sensed event intervalassociated with the value of the first feature; comparing the value ofthe first feature to the predicted value of the sensing threshold; andclassifying the value of the first feature as a predicted sensed eventin response to the value of the first feature being greater than orequal to the sensing threshold value.
 15. The method of claim 12,wherein the value of the first feature of each of the plurality ofcardiac events sensed from the cardiac signal according to the firstsetting of the sensing control parameter is a maximum peak amplitude andthe first setting of the sensing control parameter is a firstsensitivity setting, wherein the processor is configured to classifyeach maximum peak amplitude as one of a predicted sensed event or apredicted undersensed event according to the second setting of thesensing control parameter by: determining a sensing threshold valueaccording to the second setting, the second setting being a secondsensitivity setting that is greater than the first sensitivity settingso that the second sensitivity setting is less sensitive to sensingcardiac events than the first sensitivity setting; comparing the maximumpeak amplitude to the sensing threshold value; and classifying themaximum peak amplitude as a predicted sensed event in response to themaximum peak amplitude being greater than or equal to the sensingthreshold value.
 16. The method of claim 12, wherein predicting thearrhythmia is detected or not detected comprises: comparing thepredicted sensed event intervals to tachyarrhythmia detection criteria;predicting the arrhythmia is detected by predicting a tachyarrhythmiadetection in response to the predicted sensed event intervals meetingthe tachyarrhythmia detection criteria; and generating the output bygenerating data corresponding to the predicted tachyarrhythmia detectionfor display by a display unit in a graphical user interface.
 17. Themethod of claim 16, wherein generating the output comprises: determininga predicted time to detect the tachyarrhythmia; and generating the datacorresponding to the predicted tachyarrhythmia detection comprising thepredicted time to detect the tachyarrhythmia.
 18. The method of claim16, further comprising: for each setting of a plurality of settings ofthe sensing control parameter that are less sensitive to sensing cardiacevents than the first setting: classifying the value of the firstfeature of each one of the plurality of cardiac events as one of apredicted sensed event or a predicted undersensed event according to thesetting of the plurality of settings; determining a predicted sensedevent interval between each consecutive pair of the predicted sensedevents; and predicting that a tachyarrhythmia is detected or notdetected based on the predicted sensed event intervals; whereingenerating the output comprises: determining a least sensitive settingof the plurality of settings associated with a predicted arrhythmiadetection; determining a safety margin for detecting the tachyarrhythmiafor each setting of the plurality of settings of the sensing controlparameter by determining a factor of the least sensitive settingassociated with the predicted arrhythmia detection divided by thesetting of the plurality of settings; and generating the datacorresponding to the predicted tachyarrhythmia detection comprising thedetermined safety margins for display by the display unit in thegraphical user interface.
 19. The method of claim 18, wherein theplurality of cardiac events sensed from the cardiac signal according tothe first setting of the sensing control parameter correspond to adetected tachyarrhythmia, the method further comprising: predicting atachyarrhythmia detection for each programmable setting of the sensingcontrol parameter that is more sensitive to sensing cardiac events thanthe first setting; and generating the output comprises determining asafety margin for display by the display unit in the graphical userinterface for each of the programmable settings of the sensing controlparameter that is more sensitive to sensing cardiac events than thefirst setting.
 20. The method of claim 12, comprising: for each settingof a plurality of settings of the sensing control parameter that areless sensitive to sensing cardiac events than the first setting:classify the value of the first feature of each one of the plurality ofcardiac events as one of a predicted sensed event or a predictedundersensed event according to the setting; determine a predicted sensedevent interval between each consecutive pair of the predicted sensedevents; and predicting that a tachyarrhythmia is detected or notdetected based on the predicted sensed event intervals; and generatingthe output by generating a visual representation of each of theplurality of settings of the sensing control parameter that is lesssensitive than the first setting and an associated tachyarrhythmiadetection prediction for display by a display unit in a graphical userinterface.
 21. The method of claim 12, further comprising: determining arecommended setting of the sensing control parameter based on thearrhythmia detection prediction associated with the second setting ofthe sensing control parameter; and generating the output by generating aprogramming command to adjust the sensing control parameter to therecommended setting.
 22. The method of claim 12, wherein the receivedsensed cardiac event data further comprises a second value of a secondfeature determined from each one of the plurality of cardiac eventssensed from the cardiac signal according to the first setting of thesensing control parameter, the method further comprising: determiningthat the second value of the second feature associated with a given oneof the plurality of cardiac events does not meet cardiac event criteria;rejecting the value of the first feature associated with the given oneof the plurality of cardiac events from the sensed cardiac event data asbeing a non-cardiac event in response to the second value of the secondfeature not meeting cardiac event criteria; and ignoring the rejectedvalue of the first feature in classifying each value of the firstfeature as one of a predicted sensed event or a predicted undersensedevent.
 23. A non-transitory computer-readable medium storing a set ofinstructions which, when executed by a processor of a medical device,cause the medical device to: receive sensed cardiac event datacomprising a value of a feature determined from each one of a pluralityof cardiac events sensed from a cardiac signal according to a firstsetting of a sensing control parameter; classify each value of thefeature of each one of the plurality of cardiac events as one of apredicted sensed event or a predicted undersensed event according to asecond setting of the sensing control parameter, the second settingbeing less sensitive to sensing cardiac events than the first setting;determine a predicted sensed event interval between each consecutivepair of the predicted sensed events; predict that an arrhythmia isdetected or not detected based on the predicted sensed event intervals;and generate an output based on the arrhythmia detection predictionassociated with the second setting of the sensing control parameter. 24.A graphical user interface system comprising: a processor configured to:receive sensed cardiac event data comprising a value of a featuredetermined from each one of a plurality of cardiac events sensed from acardiac signal according to a first setting of a sensing controlparameter; classify each value of the feature of each one of theplurality of cardiac events as one of a predicted sensed event or apredicted undersensed event according to a second setting of the sensingcontrol parameter, the second setting being less sensitive to sensingcardiac events than the first setting; determine a predicted sensedevent interval between each consecutive pair of the predicted sensedevents; predict that an arrhythmia is detected or not detected based onthe predicted sensed event intervals; and generate an output of datacorresponding to the arrhythmia detection prediction associated with thesecond setting of the sensing control parameter; and a display unitcoupled to the processor and configured to: receive the generated outputof data from the processor; and display a visual representation of thearrhythmia detection prediction.